It's clearly a limitation of Windows (that I had heard about but forgotten long ago).
I wanted to test your example on my Windows 10 computer, but I wasn't able to enter the full name of the file, it was truncated to a fixed size. If I removed 10 characters from the parent folder name, then I could add 10 more characters to the file name.
With a quick search I've found this article:https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
"the maximum length for a path is MAX_PATH, which is defined as 260 characters"
I seem to have a problem file where the full path and filename total 275 length, this works fine when collector adds but then reports missing on missing files check.
My understanding is that Coollector makes a system call to check if the file exists, and that call fails because it can't handle a path longer than 260 characters.
Not critical for me as i will rename the folder as its messy on my side.
Very messy indeed!