Can't shift after coming to stop in 2nd gear

[konradphoto]

Hi,

I've recently bought a 2003 GZ250 and I immediately had a Suzuki shop done maintenance service on it. I told them about the following situation but they said everything was fine when I got the bike back but it just happened yesterday again: when I come to a complete stop in a gear other than the first gear, the shifter is loose and it's impossible to shift down or up. I have to roll the bike back and forth a bit to be able to downshift. I wonder if it's normal (I'm a newbie - this is my first bike) and if not, if I should be worried about it. Thanks!

btw: the bike has only +3,700 miles on it