Periodic full-resolution images from sidebar gridblock

Periodically, full-resolution (read: dominates entire page so nothing else can be seen) images will display rather than thumbnail-sized images in the sidebar gridblock. As one can imagine, this is not exactly a desirable feature.

Check http://www.douglasvanbossuyt.com for examples. Sometimes they appear and sometimes they don't. It's a matter of navigating through enough pages to get one to pop up.

My Gal2 installation has about 10-15k photos in it. I think what might be happening is that some of those photos don't have the resizes built yet (I did some bulk uploads and have been slowly processing through them over the last few months). Instead of building the resizes, sometimes WPG2 seems to just pull whatever size is available which happens to be the huge size.

Does anyone know how to fix this? It'd be nice to, at the least, contain the resolution of the displayed image, even if it does download the full-res version.