Maybe it's a duplicate of what has been reported here and there, but maybe not so I report just in case.

I have a toolbar header on top of my playlist area (separated with a splitter, and top-docked). If I reduce the height from its initial position (to ajust the pane to the toolbar height) and lock the top-pane height, the "reduced height" is lost whenever I quit and restart foobar. See screenshot below:

Before



After exit and restart





Note that everything works fine if I don't lock the top pane height.
WinXP SP2/Themes disabled.

I hope I didn't misunderstand you but you don't need an additional splitter to add a toolbar header. In Layout editing mode remove the splitter and right click the playlist --> Replace ui element --> Toolbar Header. There will be a Toolbar above your playlist without any spacing issues.

OK I'll check this evening but there may still be a bug.

Toolbar headers (especially bottom-dock ones) have some kinks in combination with locked pane height. The issue is being worked on; I don't think it is necessary to post further reports about this.

OK, that was my guess ... i reported just in case.