I just recently acquired my Avenger, and have my Faust and Avenger both equipped.
When I went into the dungeon, I started rapidly switching weapons and I noted a lagtime in the color switch of the center of the blades that occurred sometimes.

I started switching slower, and the problem persisted. It goes away after about a second, but it makes for a neat little effect on the bulge of the blade.
I've capped the effect on both swords, twice.

http://img576.imageshack.us/i/screenshot20110425at121.png/
http://img135.imageshack.us/i/screenshot20110425at120.png/
http://img815.imageshack.us/i/screenshot20110425at120.png/
http://img585.imageshack.us/i/screenshot20110425at120.png/