It sometimes does it on mine but very rarely. I tend to hit the air-con button just after a blast around the country roads as the secondary fans will kick in a pass more air through the rads. The secondary water pump will still kick in soon afterwards for around 5 mins. It may be worth while asking a garage for a quick look over the car for any obvious faults for this to happen. Possibly an airlock or a faulty temp sensor
 
i always thought that running the a/c would be good to cool the car down,but iv been told that putting the heaters on full blast at full temp is better because you take the heat out of the engine...
 
It does go off eventually, I know cos I waited for it as I was afraid it'd drain my battery :D
 
Does your fan come on for 5 mins just from turning the ignition on and off too? If so I just had this problem.
Turned out to be the Fan Control Unit located under n/s chassis leg