Collision Mask Problem

Hey all, I am having this problem where after i set the custom collision mask which matches the shape of my character, when it collide with objects, the center of the character seems to be on the far right side of sprite. Meaning when the character move to the left with obstacle, it will pass through the obstacle , when the character move to right with obstacle, it will collide before even touches it. Seems to me the whole center of collision mask is shifted to the right side. Anyone know how to solve this issue?

Show us your events, please.