"Stay on top" bug when project contains VST effects

When I load a project which contains at least one VST effect, the "stay on top" function is broken.

### Steps to reproduce

1. open LMMS
2. On the default project, add a VST effect to the master channel
3. Save the project
4. Load the project
5. Enable "Stay on top" on for instance the Controller Rack
6. Open e. g. the Piano Roll

### Expected

Everything works fine, i. e. windows interact as normal except the Controller Rack staying on top.

### Actual

If you move the Piano Roll you should notice graphical glitches when it is on top of other windows. Trying to interact with it while it is on top of another window will result in interacting with the window below.

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When you disable "stay on top", everything will work as expected again.

May be related to #4110, as this will only happen with VST effects. This bug persists after loading another project/creating a new project, just like the strange boxes from #4110.

Start by reproducing the issue with a project containing a VST effect, then enable "Stay on top" on the Controller Rack and open the Piano Roll. Investigate the desktop window interaction between the Controller Rack, Piano Roll, and VST effects. Done means the Piano Roll can be moved and used normally while the Controller Rack remains on top, including after loading another project.

Written by the indexing model from the issue text.