Is this normal

Had my cup in again today as-when you take your foot of the clutch and the revs are dying down the interior fan slows right down like its going to stop. it does this around the 1k markon thr revvs, Is this normal?
 
I think its most noticable when you pull away from a stand still with light throttle.

Probably just that when the revs drop the alternator voltage output drops and the fan in the heater is electric. Perhaps other cars have some sort of capacitor arrangement to smooth out this problem. Just a guess though