Editing time groups results in loss of data

When editing time groups, some existing entries disappear (are removed/overridden).

A likely cause for this is, that at insert the 'id' column in MySQL table 'timegroups_details' is set to the MySQL defined default, i.e. '0'. Whenever during an edit, a MySQL delete command is  executed, all entries with 'id=0' are affected, which may explain the unexpected behabior. I have not investigated the exact behavior, but the 'id' set to '0' for newer entries looks wrong to me.