V1.3.19 (456)
Using the Primitives tool I drew three circles, then deleted the bottom nodes on two of them and the top node on one of them.
Using the Drawing tool I attempted to connect two of them. I was able to connect one path from one circle to the other, but the remaining path would not connect between the two semi-circles and the corrupted semi-circle cannot be deleted entirely; one point stubbornly remains. My solution was to Undo to the point where I first drew the circles, then draw them one at a time as I came to them.
This happened on two separate glyphs several hours apart, so now I know not to do it that way, but it seems that it might be a problem.