Regarding permissions, when I have set permissions to specific group(eg:tags) seems to work fine with that group but admin group unable to read that tags and in useradmin the admin group have all the permissions needed for the tags.
Note: Before setting permissions to group, administrator was able to read tags. This happens only after I'm setting permissions for other groups. And while setting permissions for other groups I made sure that admin is not effected.
Are you talking about admin user or administrators group ?
Also, Changing one group permission should not affect other groups unless one is a member of other group.
"administrators" group has full access on /etc/tags(6.3) & /content/cq:tags(6.4/6.5) and /content nodes. This is probbaly some misconfiguration of permissions at user/group level.
Are you able to reproduce the issue on a plain AEM instance?