Ok, thank you for your patience!
I think we have tracked it down and will be testing a fix soon. It only seems to prevent stashing in Act 3, as it's not noticeable in the other acts, even though it is indeed a bug. I was testing mostly in Act 1/Act 2 when trying to replicate it earlier.
The fix should be in the next built beta (#703) which should be building in less than 8 hours or so I think automatically.