In the Schema Browser Data tab, there is one table which has the read only box checked and it can't be unchecked. The user logged on has permissions to write to the table and the table can be updated in the Editor data grid when ROWID is included in the query.
In versions 12 and above Toad now queries SYS.ALL_TAB_PRIVS. The latest version of Toad can be downloaded from the Support Portal