Wasn't sure where to - is there a bug tracker or something? I noticed that "/" is automatically changed to "_" so I'd think that it should be a trivial fix. Thanks Anthony!
Filing a bug is easy. Go to the page in Canvas with the bug (so in this case, your course's "Files" area, then click help (top right for legacy UI, bottom left for new UI), then click "report a problem."
On the form, just give them the basics. This looks like it should be pretty easy for them to understand what the issue is, but if it was a certain series of steps you'd want to describe it there.
As this is the user's community, we don't have any way to actually solve bugs. To get Instructure's attention, using the "Report a Problem" link is the best way to point out a bug.
@hsiao_62 , I'm marking this question as "Assumed Answered" because, as @abunag has stated, resolution of this issue will require submitting a help ticket to report the bug, and the Community can't fix bugs--so for the purposes of this forum, it's answered. Having said that, if you would take a moment to circle back here and update the thread with your case number (and, down the road, the resolution) it will help other members of the Community who might run across the same issue.
And, if anyone else experiences this file naming weirdness, please submit your own ticket and include a link to this discussion in the description. More reported cases makes it easier for Canvas Support to isolate the cause of a problem.