Weird error trying to add default values to tool parameters

Here's an odd situation.

Im trying to add default values to my tool parameters. Every other time it has worked fine. This time however, no matter what I do, I can't add my folder (C:\Temp\) and path to my projection file (C:\Temp\NZGD 2000 New Zealand Transverse Mercator.prj)...Well, I can add it, but when I apply those changes and open the tool, it's added a whole lot of other junk.

The default value for the projection file path, after being set to C:\Temp\NZGD 2000 New Zealand Transverse Mercator.prj is showing as C:\Temp\Temp\NZGD 2000 New Zealand Transverse Mercator.prj

I've tried to add the correct default path to the projection file a few times, and now when I run the tool, the default value is set to 'C:\Temp\Temp\Temp\Temp\Temp\NZGD 2000 New Zealand Transverse Mercator.prj'

The default value for the folder, after being set to C:\Temp shows as C:\Temp\Temp

Setting the default folder path to just C:\ after thinking I may be able to trick it into giving the path I wanted, shows as .

Any idea what the heck is going on?