Oh right, your .capx already had WebGL turned off so it was showing it working correctly instead of the error condition. That caught me out. I can reproduce if turning on WebGL.
If you have 'seamless' mode off then the tilemap will run in tiling mode which due to the way WebGL works can only deal with power-of-two tile sizes (your tile size is 120x160, the nearest power-of-two size is 128x128). Since it's not a power-of-two it has to first stretch it to power-of-two then draw that, and the stretching is where the "glitch" comes from.
If you turn 'seamless' mode on then it doesn't tile anything so the power-of-two limitation does not apply, but it still happens. This is indeed a bug because it's stretching to power-of-two sizes (which degrades quality) when it doesn't need to. This is fixed for the next build.
tl;dr - in the next beta turn 'seamless' mode on and it's fixed. It can't be worked around at the moment with seamless mode off.