files list:
a.2.txt
a.b
a.b.a
a.b.a.txt
a.b.c
a.x
Why is it sorted in this way
It's the "Sort name and extension separately" option. With that turned on, the file extension is only used to break a tie between two identical names, otherwise it's not considered at all. If you turn it off you get this:
thank you!
Set SORTNAMEEXTSEPARATELY=toggle