Looking for some advice, can’t seem to find anything specific for my problem anywhere else. 
 

VW polo 2003 1.4tdi 3 door 

So, when the interior lock switch is pressed the drivers door locks and then instantly unlocks - only the drivers door the passengers door locks as expected. I have tried replacing the switch but this did not fix the issue.  
 

The car does not have remote locking, when the key is put into the door and turned once the car locks fine, but if turned for a second time in the lock direction it unlocks the drivers door. 
 

The interior light works as expected, and turns off when door is closed and on when opened. The main issue is the interior locking switch when the lock button is pressed it locks and instantly unlocks the drivers door. The boot and passenger lock and unlock fine and the unlock button inside works as expected. 
 

any help would be much appreciated. 
 

 

The micro switches in the door locks are a common problem, if the system doesn't get a signal the door is fully latched it will then send the unlock signal, by doing from the external key you are probably just moving the mechanism slightly further so it stays locked