Hello, Raoul.

I assumed that the 'final' lunar orbit for SMART-1
around the moon was to be an orbit that would eventually become unstable and SMART-1 would eventually crash into the moon.
But ESA is talking about a "final" stable orbit around the moon
for SMART-1 after six months...Somebody has to explain
what ESA "really" has in mind.

Better still! If after a six-month science-mission around the moon, SMART-1, should use its remaining fuel to send it back
to Earth for an Earth-moon slingshot technique to send it outward to do a NEO asteroid flyby.
There are plenty of NEO asteroid candidates SMART-1 could be selected to visit.
cheers.

Jacob