I could not replicate the issue you mentioned.

Mac OS X:
almir-work:libbash AlmirKadric$ . ./regex.sh; RangeToRegex 11- 14 15; echo $?
Unkown value (11-) in range:
11-
1

Debian:
root@master3:/opt/Moria/lib/libbash# . ./regex.sh; RangeToRegex 11- 14 15; echo $?
Unkown value (11-) in range:
11-
1