I love KDENLIVE, Yet there are some very basic problems that persist through about 4 yeard, that i'm using it. it makes a lot of pain and going around problems that shouldn't exist at a such od advanced stage of this project, that's why i decided to start contributing in this way as of right now:
My suggestions that are regarding this problem, and as well those that exist ever since i can remember this project - at least 5 years:
1. Timeline structure/ the way that clips are being positioned and saved/remembered on timeline - every change in any way is messing up all clips positions, fx's applied, lengths etc.. I think the change is absolutely needed. No other NLE's have such root/basic problems when switching between different framerates, and loosing clips/fx's positions without any reason, like this bug that i am filling..
A simple saving and opening of project can loose all effects that are applied to clips.
right now i MUST create /save a new project every 15/30 minutes of editing so when at one point without any specific reason it will loose all / or any effects or cuts applied to clips - i can somehow recover and recreate work already done.
PLEASE Consider this if you ever want thins project succeed as much as i would want - whether in Windows environment, or in linux world.. it simply CANNOT be freezing, and loosing these most basic points. - HOW do other champs like sony vegas or whoever for this case do it? premiere, edius.. they'v got it down for at least 10 years..
Maybe switch to some absolute hook/ scalable/ vector/ quantifier based system for all events, and correlation system to connect fx/to specific clip as well(?),
so regardless of framerate and such it would keep precise points .. and conversions would be possible as well without loosing ALL Edits, cuts, fx's, fades, etc..
I believe it would be a REVOLUTIONARY Step, that could fix maybe even up to 30% of all bugs related to timeline/fx's problems?
2. Unable to apply speed to reverse clip.. it messes up clip and creates a thin line out of whole clip, that is unworkable.
now i reverse clip - render it out - put it on a time line and apply speed fx.
- this problem also exists for a long time
3.Edit mode on a single timeline like in sony vegas - that you can overlaps clips and set crossfade point of clip a and b - it makes it quite faster and nicer to use.
4.Playback speed - possibility of setting playback speed so there would be no lost frames - even with older machines, and on full quality - 3/4 speed, 1/2, and 1/4th should be sufficient.
5.Playback Quality - it appeared in 16.08 - which is nice - draft/ and HQ - however i do not see a big difference cpu usage is still high, and i get jerky playback/not smooth
I have an i7 processor and material is canon fullhd mov file It is not smooth regardless of whether i have 2 cores, or 8 cores, and it shouldn't be like that
In premiere/vegas it is easy to make smooth playback even in 1/4 or 1/8th original quality - and do full edit on laptop - and set it to render on stationary machine.
Especially in a era of 4k and 8k RAW source clips.. that you already are preparing /ready for-which is great- .
This option will be a VERY Important to be able to choose even 1/16 of original resolution - which will be enough for editing on a low end laptop - and than move it to Fully blown NLE Hardware..
6. if you have any recommendation/ combinantion of distro/ that is most stable and those problems do not apply / exist - please do put it up on MAIN WEb site as recommended , and put PRECISELY EACH Component, repository, number, and such, so people will have a smooth ride and not get discouraged.
7. some way of donating/ fund raising to speed up of solving most important problems.
many people have money, but do not have skills, nor time to personally help - then it should be PRIORI Visible on main page. ABSOLUTELY. I'd rather pay 50$/or 100 to fix those problems/implement to kdenlive, than spend it on sony vegas..
All of the best to THE Team!!, and project!>
Cheers!

Reproducible: Always

Steps to Reproduce:
1.put clips to bin
2.moove them to timeline
3.apply speed to clips on timeline
4.make come cuts, adjustments like in point, out point fade in out.
5.move clips around
6. save project, close
7.open project
8 move clips around, save, close project
9.open project - speed effect will be "gone" - either physically from clip effects stack, orit will be there, value will be as set, only it will not be "in effect".
However clip sizes/lengths - visual blocks on timeline will be correct, but speed and length of clip will be not correct. 
10 if you go to fx stack for specific clip - choose value of speed and add 1 poin, or substract from any given value, like 237% - change to 236% - the visual length of clip will abruptly/suddenly change - on a timeline - and fx for that one clip you'd change value will work, but the rest you'd need to do the same.
11. than you must set out point for specific clip /or stretch by clicking and dragginh right edge of clip it to previous correct length - which would be typically marked by next clip's beginning.


Actual Results:  
problem appeared, speed fx not working.
 and got partially corrected by doing the extra steps provided above / redoing the settings

Expected Results:  
Just exactly what it should. Play clip, on a timeline, at specific in and out point, specific speed, not loose settings after a simple save close and open project.

As suggested i feel that timeline system is causing all of those and other problems.

Also those few wishes/wishlist  or rather suggested fixes for problem could be a major improvement/ step forward before going to windows platform for whole project/community.

Maybe there would be a way to somehow use ready modules from other linux projects like lightworks, or shotcut?

Please feel free to contact me about anything.
I Believe in KDENLIVE To be the best and most versatile project for NLEditors

I am willing to help out, provide more info, and test it out/ other solutions to find a true cause / a possible solution, or to set guidelines / unification to higher standards for this project, and improve User Experience
.., or even pay to get those fixed/ get functions implemented / applied! :-)