SDL_PollEvent not return until tslib touching up?

I’m using SDL on a embedded linux system.
I compiled the SDL version 1.2.14.
The input is tslib touch.
I call the SDL_PollEvent function something like below:=======================
if (SDL_PollEvent(&event))
// deal event

// do something else

The problem is that:
when i touch the screen, and move my figure on the screen, the SDL
cursor moves with my figure, but the SDL_PollEvent function will not
return until i remove my figure from the touch screen. I can not
handle the touch (mouse) move event immediately.

It looks like SDL_mutexP function probelm?

Does anyone meet the same problem?
Or any suggestion?

Best wishes,