Normal for oil pressure lamp going on on the kz900 ?

I recall it was an issue on very early z1's and the sump plate was modified to the design you have now in your pics with the zig zag type baffle casting. Obviously it helped but didn't completely solve the problem under very hard acceleration, hence the swing door after market part that was made available. Interesting. Assume you are using 10/40 oil? 

I would suggest you do your testing with a pressure gauge rather than a light so you can physically see what is happening, the oil surge scenario makes complete sense however if the light only comes on when entering the "red" on a stock motor the acceleration will have tapered off at this stage (I would expect surge to be most prevalent between 6 - 9000 rpm) only my opinion

It will happen when my oil level is low.