Access right doesn't work well with subgroups

Hello,
I found a bug with right access.

I use LDAP authentication and xwiki local groups
Everyone (in LDAP directory) can read all my xwiki but only XWiki.XWikiEditeurs have write access on a space Encyclopédie.

XWiki.XWikiEditeurs contains some groups:

• XWiki.GF_PiloteM2 (XWiki.xwikilecteur user in it)
• XWiki.GF_CacP3 (XWiki.xwikilecteur user in it)
• XWiki.GF_xxx (XWiki.xwikilecteur user is NOT inside)
  this sub groups contains users.

Sometimes users of XWiki.GF_PiloteM2 and XWiki.GF_CacP3 lose write access on Encyclopédie (I didn't found the cause).
When this happen, I found a way to fix this write access problem:
I simply remove XWiki.xwikilecteur from a subgroup AND I replace him in same subgroups!!!
It is clearely a bug, isn't it?

XWiki.xwikilecteur is in this groups:

• GF_PiloteM2
• GF_CacP3
• XWikiAllGroup

and Encyclopédie space have this right access:

• XWikiAllGroup: read/comment
• XWikiEditeurs : read/comment/write
  XWikiEditeursEffac: read/comment/write/delete

Thxs.