A previous firmware used to frequently stop the beater (and maybe the vacuum?), just for a few seconds possibly as it crossed a part of floor it had already done, but the most recent FW in the XV-11 relaxed this fussiness. However, it's still likely to happen especially when, as you suggest, it's extracting itself from a tight spot. I guess that apart from saving power, it's to avoid damaging the carpet with it rubbing away in one place for too long - which may happen every time it goes by this spot when cleaning the house.
#1 Neato XV-11 SW 2.0 Board Rev 113 / 3500mAh battery pack installed May 2013 / Pet & Allergy pack installed Sept 2013. In July 2014, received and repaired a faulty #2 Neato XV-11, which also runs perfectly now