I have the same problem, i have a horizontal line between my tiled background.
I could have fix it using the point sampling but for some quality reason, i need to keep linear sampling.
It could also be a positioning error, with the two images overlapped or gapped slightly because they were placed with snap to grid turned off...
I am using snap to grid in order to position everything and this is what i get :
And with just a repositionning of 1 px, i fix the problem :
So here's my question, is it a problem with the snap to grid or there is something with my images ?
Edit: I found that on every tiled background, i have a vertical line at the top of it (you can see it all along my grass and my picks) so i don't think it is a problem a positionning.. Do you guys have an idea ?