Derivative generation goes into infinite loop

I'm running 5.2 and the latest Image module.

When I upload an image, it adds the image entry to the {files} table in the database, then creates the derivatives in the files/temp folder, moves them to the files folder, adds the derivatives to the database... then deletes the derivatives, deletes the derivative database entries, creates the derivatives, deletes, creates, etc... until PHP times out.

This happens if I create an Image node, or if I use Image_attach.