Following Mining Village, I shouldn't be able to trash the engineer for a gain twice, right? That appears to be what happens.
I just tested this and it does seem wrong, here is how it´s reported in the log
g plays a Throne Room.
g plays an Engineer.
g gains a Throne Room.
g trashes an Engineer.
g gains a Throne Room.
g plays an Engineer again.
g gains 2 Throne Rooms.
I can confirm this behaviour. Tested it also with Procession, same problem (as expected).