Guys, I bought the Glamour drum brake model an year back, but since the time I have bought it, i am finding some problems with the gear shifting.
While I shift the gear from 1st to 2nd at zero throttle after accelerating, the gear tends to stick; and now if i give a race with the clutch pedal still pressed i am able to shift.
i.e if i shift the gear at high rpm, it gets shifted. Also if i shift immediately after i press the clutch pedal, it shifts but a one second delay will cause the gear to stick.

I am facing this problem from almost the day i bought it but i initially thought that i need to get acclamatized to the bike. Also i was a new rider that time. I have also shown the problem at service station each time i give the bike for free service, but after a day or so of servicing the bike returns to the same condition.

I really don't understand where the problem lies... Please help, if possible.