Naturally, Bing is hosted on a Windows server, which inherits the Windows filesystem eccentricities. Case insensitivity is among those. Because "search" has six letters, that would mean that the robots.txt would need to have 64 entries to completely exclude this directory. That's not even including the tilde thing or any other paths to that directory. And that's for one directory.
Lame? Yes. Google's fault? Not in the slightest. But it brings up an interesting question: if MS clickstream gathering included an opt-out mechanism that happened to be impractical for Google, would that change the ethics of any of this? Say, by having the Bing toolbar identify itself in user-agent so that Google could block it if they wanted?
I wouldn't think that would materially change the situation. If Google really wanted to, they could probably "block" this now by encrypting their existing URL redirects, thus hiding the URL from the Bing toolbar entirely, at least until the user is out of the Google system.