First of all, allow me to preface this post with the fact that I am not advocating the use of IIS virtual directories in lieu of ColdFusion mappings. That is a separate legacy environment issue we're planning on addressing.
With that disclaimer out of the way, the issue that we were experiencing is with the expandPath() function not resolving properly for missing files/directories that use an IIS virtual directory as the mapping [i.e., expandPath("/myMapping/myMissingDirectory")]. This was a non-issue in ColdFusion 9.
This issue was present in ColdFusion 10 with ColdFusion mappings, but it apparently was fixed in the final build of ColdFusion 10 (I verified on my version which is running update 11).
The behavior that is happening is that if a file/directory in expandPath() does not exist CF is resolving the root mapping as starting at the root of your site directory (again, this is currently only an IIS VD issue).
For example, if you have a site directory of C:/inetpub/wwwroot/mySite and have an IIS virtual directory of myMapping that points to C:/inetpub/wwwroot/myMapping and you try to use expandPath() on a file/directory that does not exist then CF resolves the path as C:/inetpub/wwwroot/mySite/myMapping instead of C:/inetpub/wwwroot/myMapping as I would expect.
The fix for this is to use expandPath() on a directory you know will exist and append the rest of the path as in expandPath("/myMapping") & "/myMissingDirectory".
Since people should really be using ColdFusion mappings within CF code, I don't feel like a ticket should be created; but what do you all think?