The reason for that is the use of lowercase letters for the pieces. According to the Standard algebraic notation, you must use, for instance, Nxe5, instead of nxe5, no matter you are playing white or black. However, the program should be more assertive when a lowercase letter is used, instead ob showing the inconsistent behavior that you report. I write it down for future improvement. By the way, this issue is not new to 6.1.2, but comes from previous 6.x.x, possibly from 6.0.0.
Regards,
Antonio Ceballos