Thank you. I've committed your fix. verbs_to_mask() adds bits to an existing mask.

(...) I'm not sure why this only manifests on 64-bit architectures, as my reduced test case (can provide if necessary) also fails on 32-bit architectures.

Probably just a coincidence: There happens to be a 0 on the stack where the compiler puts the m variable on on your 32-bit hosts.