Edits can be seen in history. I've revised my understanding of the issue, and have removed my original mistaken understanding so it's easier to read.

This sometimes occurs when going out of focus or back into focus. Sometimes it just flickers into bilinear filtering and doesn't completely revert; other times it will completely convert and not be corrected until refocusing.

This appears in both build 5988-2cb5a08 (the latest build as of this writing), and 0.8 beta 1. This does not appear to occur in 0.7.3. A bisect may be a good idea.