Consider the Tirėlat verb lari-. It's a stative verb meaning "ready". 
Like other verbs of its class, it's intransitive, and can be made into a 
transitive verb by adding the suffix -ku.

lariku "to prepare (something), to ready".

Transitive verbs can be put into the passive or middle voice. But the 
passive voice suffix -ru and middle voice suffix -mu are in the same 
slot as the causative suffix -ku, and displace it.

lariru "to be prepared (by someone)"
larimu "to prepare (oneself)"

So what it looks like is that these are passive and middle voice forms 
of an intransitive verb. The question is: does it make sense for an 
intransitive verb to have voice? Or should these be treated as having 
underlying forms *larikuru, *larikumu?