Canvas is low resolution unless paused and resumed

I'm working on a game, and am using multiple Canvases for my menu. I press the options button, the first alphas out and the second alphas in. First is disabled, second is enabled, all is well.

However my problem lies in the fact that I have UI Text and Buttons on both Canvases; the first renders fine, but the second is terribly low resolution, stretched and blurred. I thought I may have broken something, so literally duplicated the first Canvas and the same thing happened. I ended up pausing the scene and resuming, and suddenly the second Canvas is now normal resolution. Go back to the main menu again with the back button, and now it has the low resolution!

What on earth is going on!?