Sheetmetal: Multiple flanges dissapear at 90 degrees

 Hi 

Basic stuff on Mac.  I create a polygon with standard 2mm bottom flange
When I want to draw 2 adjacent flanges or 4 flanges it "disappear" when set @ 90 degrees.  Tested it at any different lengths.
When I enter 89 degrees, bang it is drawn.
When I draw 2 adjucent flanges at 90 its perfect
Then it is impossible to draw the remaining other 2 flanges.

I am so frustrated....

Anybody experienced this as well?