My scenario:  I had a nice sword and shield equipped, and in my hotbar I had added my bow so I could just tap on it to switch between the two sets of weapons (sword/bow).  It all seemed to work OK but I noticed that after switching from the sword to the bow, my shield had disappeared.  Not in my inventory, not anywhere on the floor around me, just gone.

Yeah, me too, and it's continued in version 2.9.6.  I had it happen with a crusader and a skelly. 

I wish we could revert to earlier versions.  I'd take less content over bugs.  :(

I'm replicating this issue as well. In addition, the swapping also seems to delete other items I have in my quickslots. Doesn't return them to the main inventory, nor does it drop hem to the ground; just poof, as though they never were.

Also, if the "lost" item happens to be a stack, occasionally the quantity will still be displayed n the lower-right corner of the quickslot. However, the main item icon is one, and the quickslot isn't selectable.

This issue is more than a little bit irritating. But I have faith that you'll iron it out in a forthcoming release, preferably sooner rather than later. Can't wait to see the kinks worked out so that this thoroughly excellent game can live up to its potential!