Doesn't sound right to me.I've got a 10 Overdrive on a 520 Severne Formula and an 8.5 Overdrive on a 490 PX and once set up they rotate easily every time.
It may be a mast compatability issue.
Are they snap on cams or push thru type cams.
I had issues with another brand sail and their push thru cams that had me that angry before sailing that it wasn't worth going out. (Its really easy to lose it when your finger is stuck under the cam.)
Once it was rigged it rotated just fine though.
All cambered sails should rotate without having to kick them unless you are a flyweight and dont have the weight to snap them thru as they rotate.
This is the voice of inexperience speaking but they should rotate easily.

Ben , I use to run a KA 550 on my 05 Severne SSR 11.8 and from memory it was really well matched. I am pretty sure I always had the kick the bottom cam over, at least most of the time, even on my 11.0 which I rigged on the correct Severne mast.
Cams popping off is often a sign of insufficient downhaul. Are you pulling enough on? Big Formula sails need alot.

mr love is probably spot on. Downhaul or the lack of it does seem to affect the bottom camber first. Have you got the correct amount of spacers between the batten end and the camber?Is the luff pocket loose at that point? The luff pocket should be a neat fit around the mast,not too tight and not too loose.

I still have issues with kicking thr bottom cam/batten to make it rotate properly.
All our overdrives from 10 to 5.5 rotate without kicking them and we use Severne,Powerex,Challenger and North masts.All rig differently, some not perfectly but they all rotate properly.

It can be frustrating doing the initial setup but once done its done for good.

I got the Ka 550 so that I could rig my 2005 Severne 11 on the correct Severne 2005 530-34 and the 11.8 on the KA. I experimented with both masts. The KA was definitely stiffer overall and maybe marginally more flex top( but bugger all in it) In my opinion both sails set perfectly on the KA if not better.( By better I mean marginally fuller down low which is how the new generation of Formula sails set, the 2005 SSR 11.0 is a fairly flat sail compared to newer Formula sails)The discaimer here is I think the KA 550 is a bit too stiff for the 11.0.
I had a look at the www.peterman.dk website where he has measured bend curves. The only 2005 Severne Race mast listed is the 520 which has a bend curve of 14.3%. My experience with the other 2005 Severne Race masts would also suggest to me that the bend curves were more in the 14% range than the 12%. Severne may now be using true Constant Curve on the Redline masts, you would have to ask them.
Whether this bend curve difference is causing issues--?????? but I did have to kick my bottom cam around on the 2005 SSR 11 and Severne Race 530 most of the time. Never had them pop off though.

Thanks full moon - the issue was around the cam spacers (or lack thereof)

Will have to either make some up in flexibile traffolyte, or try and purchase some to suit this '05 sail