So it appears that Google have fixed the blurry map issue with the 3.9 / 3.10 API, which is great.

But there's a new one with custom markers. As soon as you zoom in one level, the custom markers become corrupted / blurry. They rectify themselves if zooming out, although the process of zooming out also makes the markers slightly blurry.

The 3.8 API does not exhibit this problem with custom markers. Here's a picture illustrating the problem (I suggest you open the image in a new tab; the blurriness isn't as easily visible when the image is scaled to fit this post). The blurring is most noticeable with the straight lines of the paper crane marker:

I've had a prod through the HTML, but I can't really tell how the markers are placed on the map. But I thought that I'd put this issue out there for anyone who has experienced similar, or if anyone has any thoughts on how this can be resolved, save waiting to see if it's a glitch in the API.