Stained Glass flickers/flashes sometimes

Sometimes as you walk past glass it will flash, as though the texture is changing transparency?

This has happened with and without texture packs installed.

Unable to reproduce consistently so I'm unsure of exactly what's causing it. Attached video shows it only happening once, but have seen it happen 5-6 times in a row.

Screenshots from video to show difference in the texture:

normal:
the two frames of flashing: