I use MOS on daily basis on a PB 1.67 too, but for me it works really well.
There are some freezes sometimes, but no too often.

I think, the reason behind the misterious file disappears are just a click away: The default view mode is 'icons only'. If you put anything on windows, there will not have an Amiga style icon, and will be hidden. This might look like a bad behaviour, but consider, that you can hide all, what you not really want to see always.