So I've just triggered this, and while it resembles a couple of those in the bugs list on the wiki, I thought I might add it along with how I think I caused it.
The bug was triggered on picking up 'The World' card in the Womb II, after I'd spent a fair bit of time in an arcade feeding coins to a slot machine. I fed 80+ coins to the machine and left more than a dozen heart pickups lying in the room; I've had at least two other arcades this game, possibly more. The bug caused my game to freeze for roughly a minute, then resumed, showing the card pickup animation, along with the text popup and animation on the Q icon in the top right corner. There's also a flicker show of what I assume to be every single item in the game cycling repeatedly in front of the character's face. The character sprite itself isn't moving at all.
I have three 'pretty fly' pickups, and a meat cube (which replaced one of the fly animations), along with the dead bird (playing as Eve). I have Brimstone from the first Womb level, and quite a few passives active from game progression. The arcade game master/beggar gave out more than twenty keys and bombs each, and a large number of coins; I also obtained hearts and spawned a large number of flies through the arcade game, and obtained Skatoli.
I think the bug was caused by a memory issue relating to the arcade room. Including the most recent, I know I found at least two, possibly three, in previous levels without dying, and spent at least twenty coins in each, though the last is the only one I left drops in.
Am I right? And if not, what's happened?