Michael
here a step by step :

Open MoI V4
Draw a rectangle for example (all is Ok, all the draw tools works)
Hide MoI (not quit)
Go the Finder or other apllications
Go back to MoI
Choose Rectangle tool or other draw tool
Clic to draw , drag have no effect
Result : no icon tool and panel stay empty (sse my screenshot)

Solution :
clic on Icon Moi V4 in the Apple Dock bar (click anywhere in the window don't work)
choose a draw tool

Bing ! i can draw again.