When pressing Alt key to temporarily turn off snapping, it could be turning off also curve closing.

 From:  Michael Gibson
5338.4 In reply to 5338.3 
Hi Brian, it's intended that holding down Alt should suppress all snaps temporarily and allow free placement of points while it is still held down.

But the initial question sounded to me like a bug report that holding down Alt does not suppress the special "Closed" snap.

My reply was that I've just now fixed this up so that in the next v3 beta holding Alt will also suppress that one as well. You won't see this in action until the next beta release though.

Hope that clarifies, please let me know if I did not understand properly.

- Michael