There's no difference in the way that PB7 and PB12.5 handle the stored procedure. Are you sure you are comparing apples to apples? If the procedure get invalidated and you "recompile" it, any active session would get a ORA-04068 error. However, a new connection to the database would not get the error. The error only occurs when the package is recompiled while there is an active connection.
It that isn't what you are seeing perhaps you could elaborate further. For example, you haven't indicated how you are calling the procedure (e.g., embedded SQL, RPCFUNC or datawindow stored procedure data source), or what happens for you when PB7 attempts to use it.