>> Unrelated, the "o" modifier is useless if you don't do interpolation, and it's quite silly to use on qr//. You're just asking for trouble by using it.

Understood. These are being migrated from a long if/elsif chain. The qr was just added, and I hadn't take off the /o. This stupid bug took me some time to work out. The code comes from a file with a fair number of RE's that do include variable interpolation; adding /o on all patterns was for my convenience at detecting patterns with interpolation that *didn't* use the o option.