This behavior is only present when the Package Spec and Body is loaded from the same saved file i.e. the following option is checked:
View | Toad Options | Editor | Open\Save | Automatically save Spec/Body when saving object to file
WORKAROUND 1:
Manually change the SQL script tab desktop to SQL (Recommended)
WORKAROUND 2:
Uncheck option Automatically save Spec/Body when saving object to file (Note that any files saved prior to the change of the option, will still show this behavior)
STATUS:
Waiting for fix in a future release of Toad for Oracle