I have used this (A) left sidebar for extended time:
If I quit Rhino in this config and relaunch, I get this (B) sidebar:
_ToggleLeftSidebar restores the (A) sidebar.
Restart and launch gets (B) sidebar as well until _ToggleLeftSidebar is invoked.
Seen on 3 separate 10.12.6 5E199w Macs with same com.mcneel.rhinoceros.plist