Hi,
*call method o_super->m4. "throws syntax error.
but when i change this to m4 in brackets:
call method o_super->('m4'). "works fine WHY!!!!!! (atleast no syntax error)
but the prog dumps.
Basically what is the diff between two above statements.
What you have written by adding brackets is a dynamic method call. Syntax checker is is no run-time environment and the correctness of dynamic method call will not be evaluated until run-time... That's why syntax error goes away, and run-time error comes.
And, obviously, nothing in the call is working "fine". If you will change the call to call method o_super->('M4')and will not overwrite o_super by recreating it from static type vehicle, the call indeed will work fine 
For the difference between static access and dynamic access read Accessing Class Components please.
cheers
Jānis