When you display a Stored Procedure in AQT, you can see:
There is one little trap with these - the system table that holds the procedure parameters is only populated when the procedure compiles successfully. So, if your procedure has not yet compiled OK, you can see the text for it in the Database Explorer, however the parameter-list will be empty.
When you create a new Stored Procedure, you enter the parameters on a separate tab in the window. However when you display or modify the procedure, you will not be shown this tab. This is because, if your SP has not compiled successfully, the parameters can not be shown. Instead you are shown the full procedure text