The code that intended to have mimics occasionally take on the form
of "strange object" always produced downstairs instead because
S_MIMIC_DEF is greater than MAXOCLASSES.
This problem was present in 3.4.3. I didn't try to go back to see
how long it's been there, but strange objects used to occur once
upon a time. Either nobody noticed that they'd gone away or there's
an alternate way to produce them.
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