SUMMARY
Image files with a colon in the filename are reported as "invalid" in the clip monitor when the project is [re]opened.

STEPS TO REPRODUCE
1. Create a project (test project was 1280x720, 30 fps)
2. Import an image with a colon in the filename.  It will seem to work.
3. Import an image without a colon in the filename (using a copy of the same clip from step 2 is illustrative).  It will seem to work.
4. Save the project.
5. Close the project (by closing kdenlive or opening a different project)
6. Open the test project. 

You can insert the clips into the timeline.  Or not.

Sometimes kdenlive will crash when trying to open the test project (especially after several open/add-images/save/close/open-another/close/open-test cycles)

OBSERVED RESULT
The image with a colon in its name is "invalid" in the clip viewer.
If you added it to the timeline, it *may* appear distorted there.

The image without a colon in its name works as expected.

EXPECTED RESULT
All imported clips appear, without distortion, in every use.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: appimage
KDE Frameworks Version: appimage
Qt Version: appimage

ADDITIONAL INFORMATION

PopOs 18.04 (Ubuntu derivative) running 19.04.3 appimage

This *may* be related to bug 377131