Hello! I've noticed this sort of stuff happening for awhile in Krita: http://i.imgur.com/RrSrEVR.png

What causes the really jarring transitions between values?

Might be the limits of 8 bits per channel.

Krita doesn't try to fake inbetween colours because it can handle 16bit per channel. I recommend you give 16bit a try, though, it will make your files a lot larger and some operations slower. It is the price for better colour precision

You can afterwards convert back to 8bit per channel for web.

I'll give that a try. Thanks for the reply!