Because for several minutes, a certain comment's talkscreen.bml worked as expected, but deletetalk.bml gave the error "The comment doesn't even exist..."
Consistently, albeit for a brief period, the one worked while the other did not.
(Actually, it was two comments, both of which had just been posted. So it seemed like an ordinary replication issue, except in how consistently it persisted; so I'm wondering if it was an ordinary replication issue, that might have been compounded by the memcaching.)
If I'm being stupid, thwap me.