Questions Changing Bearings

Hi there,
i am new to fontcreator and i was playing a little bit with bearings.
when i change a single character by 10% each side the value is correct,
try font arial character M lsb=152 an rsb 155 → bearing 110 value is lsb=167 and rsb=170
but when i change the whole characterset by 10% each side the value is higher.
try font arial character M lsb=152 an rsb 155 → bearing 110 value is lsb=184 and rsb=188

ive looked into the manuals but cant find anything what would help me to understand this

btw: i am using fontcreator 14

thanks a lot
m

i think i found a bug ..
when a singe character from the font is also open in a tab this issue happend, when i only open the font and then make the bearing all looks fine and correct.

hope this could help

m