Yeah it's all point filtering. Gotta have that pixelly goodness...
Problem goes away if I use 'good' or lower quality setting. I tried adding some padding before I found the quality setting thing but it didn't seem to help.
I tried again, y'know, for science, set quality to fantastic, go to the spritecollection with my tiles in it, change Extra padding to 1, apply, commit, no change. Set it to 16, apply, commit, no change.