That's not preferred behavior for ground targets. Keeping on attacking a ground target while moving has always been possible (shift-move command while attacking ground) and only in rare situations was that used or useful. Whereas attacks on ground that you want to end by a move command happen every game.- partially revert the "lock-on targeting" behavior:
If a user-selected target moves out of range, the lock is
now broken as it used to be and automatic targeting is not
blocked anymore (though this can take some SlowUpdate's).
For ground-attack orders it is still in place, since the
behavior seems to be preferred (so a unit that is told to
attack a position and then to move away will keep firing
even when other targets are available)
It is also quite confusing for people not aware of it, see for example
http://springrts.com/phpbb/viewtopic.php?f=44&t=28632