Yea I guess it's kinda broken. I tested it with floating toolbars and it works, but it can't remember docked ones in some cases...lame.
But since we're talking about Reaper here, there's almost always a workaround. All hope is not lost.
In this case, since the top toolbar reports a toggle state, you can use cycle actions to show/hide it in combination with whatever can be saved in screensets, like so:
IF NOT
show/hide toolbar at top...
show/hide toolbar at top...
Load window screenset X
END IF
---step---
IF
show/hide toolbar at top...
show/hide toolbar at top...
Load window screenset Y
END IF