A Regex with multiple groupings can cause descriptions and comments to cahnge:

Eg.

With jira.projectkey.pattern = ([A-Z]([A-Z]|[0-9])+) the following can happen:

29DEB932-7983-1000-A514-C0A878320001 becomes
29DEB9322-7983-1000-A514-C0A878320001 (extra digit "2" before hyphen)

An extra "2" before the hyphen

The below examples also illustrate the problem:

ABCDEE-7 becomes ABCDEE-7 (no problem in this case)
2BCDEE-7 becomes 2BCDEE-7 (no problem in this case)
2A21-7 becomes A211-7 (extra "1" before hyphen)
A22-7 becomes A222-7 (extra "2" before hyphen)
A1-7 becomes A11-7 (extra "1" before hyphen)
A-7 becomes A-7 (no problem in this case)

It is caused by the extra groups.
This shouldn't change data though, the above regex can be written as jira.projectkey.pattern = ([A-Z][A-Z0-9]+) and will perform correctly.