`compgen -A file -G './tmp/*.sh` unexpectedly shows ALL the files in directory ./ as well as the desired ones

I expected that

compgen -A file -G './tmp/*.sh'

would show only files under tmp/, but it also showed all files in the current directory. I have tried

compgen -A file -X  '!(tmp/*.sh)'

and

compgen -A file -X  "!(tmp/*.sh)"

but both result in null output. Checking settings:

$ shopt|grep extglob
extglob        	on

It's also worth noting that

compgen -A file tmp/*.sh

returns only the first valid candidate. Incidentally, this exactly matches the default line completion result, e.g.

cp tmp/*.sh[TAB]

and

ls tmp/*.sh[TAB]

both expand out to only the first candidate. Two questions: 1. Why? 2. Any way to get the expected result using only compgen? The 'expected result' is for all the matching candidates to be returned, as would happen with ls tmp/*.sh