I use Windows 7 x64. You can try this on your computer, too.
Go take any file. Try to rename it to 'aux.svg'. Windows will answer with
The specified device name is invalid.
I tried this on two different computers (also Win7 x64), with the same results.
You can take any file you want. You can not rename it to 'aux.svg'. Dropbox will not download a file with that name. The browser will rename it to '_aux.svg' when downloading. This seems to happen in any directory I cared to try.
What the heck is happening here?