Picture would help but I assume you mean the after closing the sliding panel opens itself slightly and the gap is at the wall after the panels slides? I fthis is what you mean that is not normal and typically I beleive it would mean that the system is not level or square.

I was also going to suggest that the doors are not installed level. On the older style of slider or bypass doors you were able to adjust the roller bracket to bring to doors into level. I'm not sure what adjustments are available on the newer type of slider, which I assume is a set of rollers which roll on a bar. I would start by checking the level of the bar.