Built a vat via the construction menu, crafted some rum wort (not enough to fill the vat), put the rum wort in the vat, and let it sit whilst I crafted up some vodka wort (partial-fill again).  Built a second vat for the vodka wort, loaded it, started both up, and when I checked ~6 hours later, problem.

It also works just as well if you debug in enough wort to fill the vat, then examine it.  You fill the vat just fine, then examine it again: the screen flickers and nothing happens.  Examine a third time, debug message (it's empty!), blank screen, and BAM it's an empty vat.

Neither of the other PRs touched iexamine.cpp.