Silverlight Breakpoints Not Being Hit?

After rebuilding my machine I found that breakpoints on the Silverlight 1.1 project I was working on were not being hit. All worked fine in the same project before the rebuild. Much head scratching (is that event handler even executing? okay, let's put a breakpoint somewhere that *must* get hit. hmm) ensued.

Problem solved when I discovered that the Silverlight debugging checkbox in the website properties had mysteriously unchecked itself...