My car has shifting the gear problem.

Hi there, I have been in a trouble to find out the problem with my car. My car make is Nissan Sunny 1.3. I have a problem with the automatic transmission. Whenever i stop my car at signal or whatever, gears do not change from 1st (D) to 2nd. To solve this problem, i have to completely stop my car, switch off the engine, wait for some while then start again. I even can not accelerate my car rapidly from 0 kilometers to so on because i fear about getting stuck of gears. Please help me out from this problem. I went to mechanic but even he did not find anything because this problem happens not regularly. It happens specially when i completely stop my car to 0 Kilometers. Thanks!