I got the same tagging error as jmone when I tried to duplicate this last night.
To clarify some misconceptions in this thread.
The path
D\folder\filename.ext
is not a network path, but is a relative path, relative to the process' current directory. If MC created the path "D\folder\", it would be under one of its directories (I haven't looked at MC's working directory while it runs), and the file filename.ext would be there, under D\folder\.
However, the field being replaced is Filename (path), and MC has some code to catch changes to the file name and file path. So we don't know exactly what it does when an absolute path D:\folder\ is changed into a relative path (D\folder\). One of the dev's would have to comment.
It would be ideal if the code that traps changes to file path/name could warn ahead of time about illegal or unacceptable values.
I'm not so sure about allowing changes to Volume, Filename, Filename (path), and Filename (name) in Find/Replace. I think rename, move, copy operations should be supported only via the Rename dialog (adding any currently missing functionality required to support abilities in Find/Rename). These fields are not merely database properties or tags, but are physical file system values mirrored into MC. And physical path/filename manipulation like this should be handled via the UI in an unambiguous way, clear to users.