All,
this relates to Beta 13.0.0.41 of Toad for Oracle.
I changed a package body, then hit F9 to compile.
The bottom status line indicates I have created 20 errors and 0 warnings.
The errors tab of the messages pop-up shows an empty list of errors, though.
And yet some lines in the edit panel are marked with an exclamation mark in red.
Without the actual error messages it gets kinda impractical to get the package to compile again 
I tried closing the messages pop-up and recompiling. Unfortunately, the issue persists.