Might try double clutching. Shift out of first, let the clutch out,
push the clutch back in and shift to second gear as you would normally
do. Used to work in the good old days.
Has it always been doing this or did it just start doing this? If
it's been that way all its life, then maybe the mechanic is right and
that's just the way it's designed. If it's just started doing this,
then something has changed. If it is a problem, lean mixture could
cause it but the only way to track it down is to put a scan tool on it
and watch the fuel trim under varying conditions. Good luck. Al