Cant open in in mid air or on half slabs. On latest versions.

didnt know about half slabs..mid air is intententional..if you're building a bridge by crouching+walking backward and placing blocks, this would normally cause the GUI to open and the player would fall (likely to their death)..i'll look into the slabs

Ok good point didnt think about that
The whole falling thing anyway

fixed the slab issue in dev