I was trying to reproduce it with boxes, and saw something what maybe is doing the speed different from 0 when in collision with a wall.
It's straight related to the collision detection. When I have the time I'll work on it to see what's happening to show here.
EDITED:
Ashley, I found the cause.
When you make a new sprite object, import frames of different sizes and edit it's collision box inside the editor, it'll keep the size of the first frame, and the collision box will set the percentage of this first collision box too.
I found it accidentally after this issue: scirra.com/FORUM/shaking-screen-and-player-position_topic54555.html
Where I started a new sprite and after loading the image inside the editor, it keeped the old size for the collision box. It explain why the hell on a standing animation the character is moving a very little bit, keeping the speed different from 0.
Re-cheking my main project, where the player have a lot of animations, I detected some animations was imported with different sizes and after this, I just edited the images outside the software to maintain the same size of the very first frame, but when re-loading them, they keep the old size for the collision box, even thought showing the right coordinates on the editor.
I solved it exporting the project in folder and editing all the files where this sizes and percentages are presents.