Ii it a bug?
Have you followed what it says in the manual:
[quote:1xdjkf5c]Seamless mode
Use a rendering mode that prevents seams appearing between tiles, but also disables some tilemap optimisations which could reduce performance. Turning Seamless mode off can improve performance, but may show seams if the following project properties are not as follows: Letterbox integer scale fullscreen mode, Point sampling, and Pixel rounding on.
If you have, then it could be a bug, but best check.