Maybe the MT4 bridge expects a 4 byte value which is enough to store 8 digits, whereas for 10 digits you need an 8 byte value.

MT4 account value is 8 bytes (long).

https://docs.mql4.com/constants/environment_state/accountinformation
https://docs.mql4.com/basis/types/integer/integertypes

Thus "25400000412" could be a valid account number.