Launcher no longer accepts network path for game directory

When the 'game directory' is set to a network path, the following error is displayed when launching the game:

"The game directory is invalid or inaccessible.
Error details: The specified path is invalid
Filename on disk: .minecraft
Path: \\dell\Profile Data\dan\Application Data\.minecraft
Exists: directory"

I have verified that this is an issue with network paths, by mapping "\\dell\profile data%USERNAME%\application data" to a network drive (A:). I then set the 'game directory' to "A:\.minecraft" from the launcher. This resulted in no error being returned, and the game subsequently launching successfully.
I have tried the workaround on two other client computers on my network with the same outcome.
This also verifies that this is not an issue with directory permissions, or security settings from within Windows.