Instrument window width is incorrect, shows unintentional background tiling

[rubiefawn]

Some instrument windows are wider than they should be (most of them are designed for artwork that is 250px wide). This causes the background artwork to visibly repeat. The amount of extra width appears to vary from user to user.

[regulus79]

I have had difficultly tracking down the cause of this. However, I noticed that it only occurs on ZynAddSubFX, OpulenZ, and VeSTige. Also, while it does occur on my self-compiled build, I noticed it did not occur on an appimage build while I was testing a PR (I can't remember which one).

I am on Arch Linux, GNOME 47, Wayland (though I suspect lmms doesn't use wayland).