This request is already fixed in upstream FreeIPA project. Please refer to the linked ticket for additional details and related commits.

In UI, ran tests below:
1> Add user (and host) in single usergroup (and hostgroup) using regex set for usergroup  (and hostgroup)
  - added two usergroups/hostgroups
  - added two automember rules for the groups above
  - added automember conditions where class=<str>
  - added user/host and set class to be the str
  - verified the user/host was in the right group

2> Add user/host in multiple usergroup/hostgroup using regex set for group
  - added user/host in above setup, with multiple values for class
  - verified the user/host was in the right groups


3> change usergroup of user using "class" parameter to another group
  - updated a user/host added above to use another class
  - rebuilt automember rule
  - refresh
  - user/host group membership is updated correctly

Verified using ipa-server-4.1.0-15.el7.x86_64

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2015-0442.html