file paths tend to get converted when they have special characters, which is why they don't let you use some in most file systems. As they end up being used for system breaks like / for folder hiearchy. I know in some systems, the underscore when doubled up ends up actually becoming an escape character when transcoded. Not sure that is what is happening here, but have seen it before where you have to special character escape doubled up special symbols such as an underscore.
Where that becomes a problem, maya, max, or HE export not sure.
In any case it's a good find to know about.
Thanks for figuring it out and saving others time. and frustration