You also get this problem if you use your own http handlers and for example use the ashx-extension for this handler (or any other extension than is not hardcoded into the ExternalUrlHandle, the hardcoded once are "aspx, gif, jpg, jpeg, png, js, htc, css, ico, axd").
You can get around this though by either turn the module off compelytly (which seems to be the best option since this module seems to be pretty bad designed) or by adding this undocumented(!) configuration to your web.config and exclude all extensions in the value-attribute that is used by your http handlers:
<add key="EPsExternalUrlHandlerSkipFileTypes" value="aspx, gif, jpg, jpeg, png, js, htc, css, ico, axd, ashx"/>
Thouse stored procedures do unindexed table scans as soon as a file with an "unknown" extension is called that either is treaten by another http handler or is missig on disk (goves 404, which can case any big site to complety collapse if you get lot of requests to http-handlers or files that do not exist on disk.