CMD+minus can't be used with FX chain window open

I assigned "Show/Hide envelope for last touched parameter" to CMD+- and it works when a vst is floating, but when inside the fx chain I get an error.



Assigning the action to a different shortcut like cmd+= is fine. Minus by itself works but you have to click into the arrange view after moving the fx control.

Reaper v5.23
OSX 10.10.5

CMD+minus can't be used with FX chain window open