kdenlive-git 15.12.0.r6719.1443863-1
mlt-git r4152.v0.9.2.374.g6b518f5-1

Steps to reproduce:
1. Start kdenlive
2. Import video
3. Add video to track
4. Add fade from black effect to track,
5. Look at properties
6. Change duration to 10 seconds
7. Click in the timeline, Play back track, click on track
8. delete the effect

Expected result:
5. -> duration has the default value
7. -> The first 10 seconds of each track are fading from black, shorter clips either don't fade or fade, with the value reduced to the clip length. Track effect has duration 10s.
8. -> effect gets deleted

Actual result:
5. -> duration is 0
7. -> in properties, duration resets to 0, fade appears to not work, the entire clip seems to be black or fade
8. -> effect doesn't get deleted, however you can save, close, reload and it will be gone.

Alternatively, the ability to add the effect to tracks could be disabled.

Video:
https://youtu.be/CkvgeWcV7ig