[Plugin: Sociable] Missing Tumblr Icon

I upgraded my Sociable plugin and noticed that several of my icons were missing: TwitThis, Furl, and Tumblr. I deleted Furl because no one ever used it, and changed TwitThis to the Twitter icon. That just leaves Tumblr, which still won’t appear correctly. See here at the bottom of my post:

http://www.wasabimon.com/archive/how-to-make-vanilla-sugar/

If you look at the code for the page, it lists the directory for the image but not the actual file name itself. I’ve checked the image directory and the tumblr.png is there with the correct permissions, so I can’t figure out what the deal is.

How can I fix this, and why did it happen to begin with? It’s actually been this way since 3.2 (I think – don’t remember exactly which version) but upgrading to 3.3 didn’t fix the problem like I hoped it would.