[BUG] The button click is not handeled until the mouse is moved

[iv-m]

Describe the bug
If I'm careful enough to click any button (Settings, Free/Sync toggle, presets, ...), it does not work immediately, but only later when I move the pointer.

I first discovered this when clicking the settings button on a touchpad: the menu did not appear at first.

I see the same behavior with LV2 plugin in Ardour 7.5 and standalone application connected to Jack; both with release linux deb 1.3.0 downloaded from releases pages here and the develop branch (commit e78920a) I've build myself.

To Reproduce
Steps to reproduce the behavior:

1. Go to ChowMatrix GUI
2. Click on settings menu carefully, avoiding moving the pointer at the same time
3. See that the menu does not appear
4. (optionally) Wait a few seconds -- menu still does not appear
5. Move mouse pointer up a little bit -- the menu appears

Expected behavior
A menu appears immediately after I release the mouse button.

Desktop (please complete the following information):

• OS: Linux x86_64
• DAW: Standalone version, LV2 in Ardour 7.5
• Version: 1.3.0 (from release deb), e78920a
• 32/64 bit: 64 bit