problem with the size of staffs (solved!)

A composition is ready for publishing but after printing out I saw that the staff in one flow a little bit smaller than is the other flows. I had set the spatium size for the full score to 1,65 mm. I didn’t change intentional the size of the staffs anywhere (and I checked that again). The difference is small, but visible. If I set the score size to 1600% the smaller staff has a diameter from 7.9 mm on display, the staffs on the other flows are 8.3 mm.
What I’m doing wrong?
I only know two possibilities to control the size: The spatium size for the whole project and for every flow via Edit : Staff size.

You can also change staff sizes from any Frame Break or System Break. Could you have done this, somewhere? Click through your System Breaks and Frame Breaks and see if any of them have this property set.

Thank you very much! This was the problem!