When I'm doing remote debugging and I have the local project selected, if the local version of the file is not the same as the remote version of the file, it shows the local file with the execution point at the wrong place (because the code has changed).

Is this a bug? Why is the remote debugger showing me an invalid file?

IDE shows the file available in the project.
IDE does not see your remote file.
Same goes to the debugger. It sees its local file which is remote for the IDE, and it does not see the remote files (which are local to the IDE).
It is not a bug.

To avoid problems with file content, keep it synchronized. Either upload the changes to the server, or download the changes from the server, or work with remote files using Samba or Windows Share.