Secondary categories number 254 limited?

I have a cell phone accessories sale website, i use the secondary categories function to link the accessory to every compatible cell phone model(as category). But i found a problem that the max number of Secondary categories is 254. if you add more the main category will dispear in 'General" part and the product can’t be saved. If you choose main category again, you could save the after that, the main catefory dispear again.

Is there a max number limited? Any way could fix it?

Thank you.