>>If tables are huge then the first form will take more time to load.
>>After it loads VFP cache everything and Form B loads much more faster.
>
>I did it the other way, started form B first (1 second) and form A later (30 seconds)
>form A always takes 30 seconds while form B only takes 1 seconds, no matter who start first.

Have you tried running with Event Tracking to see whether different events are firing? How about with Coverage Logging, so you can check whether the same lines of code are firing?

Tamar