Created attachment 154910 [details]
The Lift/gamma/gain effect after collapsing and expanding it back again

SUMMARY
The widgets of some effects (like the wheels of Lift/Gamma/Gain, and the slider of White Balance and White Balance (LMS Space), disappear after collapsing the effect and expanding it back again.

It does *not* happen to all effects, only a handful, it seems.  But I haven't tested all the effects, so I don't know which and how many are affected.

The widgets are back if I do this: 1. Keep the effect expanded; 2. Add another effect to the clip or move any effect up/down in the stack. But it's only back until I collapse the effect again.


STEPS TO REPRODUCE
1. Add effect (Lift/gamma/gain, for example) to a clip;
2. Collapse the effect, then expand it back again;
3. See how the Lift/Gamma/Gain color wheels are gone;

(additional)
4. Add another (any) effect to the clip;
5. See how the color wheels are back in the Lift/gamma/gain effect;
6. Collapse the Lift/gamma/gain effect again;
7. See how the color wheels are gone again.

OBSERVED RESULT
After collapsing the effect and expanding it back again, the widgets, such as color wheels and sliders disappear from the effect.


EXPECTED RESULT
Collapsing & expanding an effect should never make its widgets, such as color wheels and sliders, disappear from the effect.


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Pop!_OS 21.10 (GNOME 40.4.0 under X11)
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 5.100.0 (found in "About Kdenlive")
Qt Version: 5.15.7 (found in "About Kdenlive")

ADDITIONAL INFORMATION