Recently, 47 MathML bugs were fixed in WebKit in a crowd-funded effort by Frédéric Wang.

When will we be able to profit from this for Prince XML MathML rendering?

Prince doesn't use WebKit, so...

Sorry, Michael. I completely forgot that Prince has its own layout engine.

I must have mixed up with Håkon Wium Lie's other contraption, the Opera browser, which I now read is moving on to the Blink layout engine.

By the way, Frédéric Wang also did 56 MathML patches to Mozilla's Gecko layout engine.

Perhaps you could contract him to do the same for Prince's layout engine?
It is really a pity that square root signs are currently not connected in Prince's MathML renderings...