Toad asks for the value of a parameter even if it is not necessary when doing control + enter.
To reproduce the problem follow the steps below:
1)Paste the following code into the Editor:
FROM (SELECT dummy FROM DUAL) t;
2)Select just the select and click control + Enter , toad opens a pop up (that is ok so far).
3) If you click on ok then toad asks you the value for :t_0.
That should not be necessary as you have all the info inside the select.
Waiting for fix in a future release of Toad for Oracle