Access rights system cannot cope with a group name which includes space characters

With XWiki v0.9.840:
It seems to be impossible to define an access right for a group that has a space character in the web name, e.g: "My TestSpace.testGroup" .
The space character is used as a delimiter for specifying multiple groups within a single access right entry.
With URLs, XWiki does ' ' to/from '+' char conversions, but this does not seem to work for group names within access right entries (so entering "My+TestSpace.testGroup" did not work).

With XWiki v0.9.1252:
The access rights GUI generates the following 3 selectbox options from the "My TestSpace.testGroup" group:

<option value='My TestSpace.testGroup' label='My TestSpace.testGroup'>testGroup</option>
<option value='My' label='My'>My</option>
<option value='TestSpace.testGroup' label='TestSpace.testGroup'>testGroup</option>

The first one is correct, but if I select it and save the rights object, under the covers xwiki seems to select the two other options. It seems I still cannot define an access right based on a group which has a space character in its name.