Front brakes locking on

[Colinwri]

Hi, I've just bought a 2014 Crossrunner with 6k miles.  On my first ride out (400miles) my bike's front brakes, on two occassions, locked up from pulling away at traffic lights.  A light press of the front brake level and release and away it goes again.
It is currently in the service shop who have stripped and cleaned the brakes and are finding that not all the time but sometimes the pistons are not returning and are hard to return if forced.  They are about to check the lines for any kinks but have mentioned that it could be a delay valve or the ABS pump.  These items are not cheap and it seems like I have to buy the items for them to be fitted one by one until culprit found.
Has anyone had this experience and know what may be the cause?

[brucey]

Do they lock on violently like you've pulled the lever or just stick? Does the bike move freely after you've come to a stop before you pull away? IMHO it's unlikely that it's a major component like the ABS system is at fault. With so little miles on a 2014 bike I'd be inclined to just start with a new piston and seal kit in both calipers (obviously with new brake fluid) and go from there. Eliminate the cheap stuff first...