The problem persists in the latest appimage 19.04.1c and in the Flatpack version as well. A shame because I was writing some tutorials on how to use the kdenlive editor as a video composition application to make our own animated backgrounds for texts, for example, but with this new version it is not possible despite having a preset to export with transparency ... in version 18.12 I had to create a preset to export with transparency and it works wonders.

Git commit e71e7609b5b47a461f9863307f1a4a0df30d1411 by Jean-Baptiste Mardelle.
Committed on 03/06/2019 at 05:33.
Pushed by mardelle into branch 'Applications/19.04'.

Fix error in composition index for 1st track.

M  +25   -28   src/timeline2/model/timelinemodel.cpp

https://invent.kde.org/kde/kdenlive/commit/e71e7609b5b47a461f9863307f1a4a0df30d1411

Thanks for your report. There was indeed an error in the "automatic" track calculation that returned wrong results for the track just above lowest video track. As a workaround, you can force the lowest composition track to V1 insteadf of automatic and it will work as expected. Fix will be in 19.04.2 released this week.

(In reply to Jean-Baptiste Mardelle from comment #3)
Thank you very much, I am already looking forward to the version .2 :-)

It's not solved completely. Load attached Kdenlive file. 

Change from high quality mode to none: You see content of V4 only. 

Select the high quality mode again: You see content of V1 only instead of content of all tracks staggered.

(In reply to emohr from comment #5)
Effectively this happens and should not happen, I have been solving it by closing and reopening the application, but I'm sure it will be fixed and will work again as it does in the previous versions.
Thank you.

Well, it doesn't fix problem in existing projects. So you need to edit the composition between track V1 and V2, and set the compositing track to V1, then back to "Automatic" and it should work as expected after that.
An automatic detection of these cases might be nice I agree, if I find time I will try to add it and warn user on project opening.

(In reply to Jean-Baptiste Mardelle from comment #7)
Thank you very much

@RafAMar Please try with tomorrows Kdenlive_Nightly_Appimage

https://binary-factory.kde.org/job/Kdenlive_Nightly_Appimage_Build/lastSuccessfulBuild/artifact/

And apply Jean-Baptiste Mardelle comment #7

Created attachment 120533 [details]
Test track composer

(In reply to emohr from comment #9)

With this version that you indicate to me it goes well when I already have the assembly with the transition of composing and transforming inserted, but if I do not have the transition inserted when I change from none to high quality it is still only visible V1. I feel that I do not know programming and little else I can contribute ... I am an audiovisual technician and I develop well as a computer user, but programming for me is a mystery :-)
I attached a project file so you can see what happens with the different composition modes beyond the transitions.
Thank you very much for your good work.

P.S. I have seen that the problem of the preview is resuleta in this version, so I will indicate it in the bug in which I quoted this.

Comment on attachment 120533 [details]
Test track composer

With this version that you indicate to me it goes well when I already have the assembly with the transition of composing and transforming inserted, but if I do not have the transition inserted when I change from none to high quality it is still only visible V1. I feel that I do not know programming and little else I can contribute ... I am an audiovisual technician and I develop well as a computer user, but programming for me is a mystery :-)
I attached a project file so you can see what happens with the different composition modes beyond the transitions.
Thank you very much for your good work.

P.S. I have seen that the problem of the preview is resuleta in this version, so I will indicate it in the bug in which I quoted this.

Sorry I duplicated a comment

(In reply to emohr from comment #9)
Only note that when you go from none to high quality in the section that there is no transition is still giving an erroneous view and solves restarting the application.

Git commit c9358290cea048020486285844a03f617e1d064b by Jean-Baptiste Mardelle.
Committed on 04/06/2019 at 05:46.
Pushed by mardelle into branch 'Applications/19.04'.

Save track compositing mode in project to restore it on load
Fix compositing broken for first track if we have a video only project after switching compositing mode

M  +6    -0    src/project/projectmanager.cpp
M  +2    -1    src/timeline2/view/timelinecontroller.cpp

https://invent.kde.org/kde/kdenlive/commit/c9358290cea048020486285844a03f617e1d064b

Thanks again for the detailed bug report and attached project. In fact, when switching compositing to "none" and back to another mode, track compositing was not enabled for the lowest track. This went undetected since most projects have an audio track as lowest track so the bug was not triggered. This is now fixed.
I also now made a change to save track compositing mode in the project (before it always reverted to high resolution each time you opened the project.
The problem should now be fixed, and you can test today's automated AppImage build for confirmation - the build will happen in approximately 7 hours - check that it was built on the 4th of june on emohr's link in comment 9.

Ok thank you very much, I will wait for the version of June 4 to try. Then I will comment on the result. Thanks again.

Created attachment 120569 [details]
Example

My most sincere congratulations, now it is perfect, I am very happy and grateful with your good work. I have attached this file as a sample of the type of montage that I intend to do, where the color clip would be a video. So without leaving kdenlive I can make dynamic multitrack backgrounds for texts in a project and then load the result with alpha channel in my video project in a single track, or even the project in .kdenlive format. I take this to indicate that within the files supported when loaded with the wizard of the project folder have disappeared the .kdenlive. Note that I use the test.kdenlive project as if it were a video clip in the example. This simplifies video editing with elaborate and animated graphics.
Thank you very much for your concern that kdenlive is still the best open source video editor today.