"View" permissions for Groups and Individual Users is being lost on Space-level.
The problem has been reproduced with "Local" AND "LDAP" Groups on "Groups" level and only with "LDAP" users on Individual-Users level.
The problem is related to case-sensitivity with user and group names.

Steps for reproducing this problem are:

1) Create a username and group using uppercase characters in LDAP and locally in Confluence
2) Go to "Browse Space->Advanced->Space Permissions"
3) Go to "Individual Users" section and type the name of this user in lowercase and click on "Add". Please do not use the "User-Picker" in this step.
4) Confluence will correctly pick up the user and display the username in uppercase, as the user was originally created.
5) Select all available permissions for this space for this user and click on "Save All"
6) Notice that the "View" permission is not checked after saving.
7) Edit the permissions again by going to "Edit Permissions" and notice that the "View" permission is now checked.
8) Remove all available permissions for this user and click on "Save All"
9) Notice now that only View permission is checked and all others are unchecked
10) This user can now not be removed from the "Individual Users" permissions section as the "View" permissions keep toggling.
11) Repeat the above steps for "Groups", with a group name in uppercase.

Tested with "Classic" and "Default" themes.

Cannot reproduce on Confluence v2.5.7