Honestly, it could've been more of an issue with my ability to tell the difference between them. I noticed sometimes, I'd miss like a single character or I think maybe a space in the name. Really don't think it's a bug, I just had a personal challenge. I'd then go back to delete it and just wasn't sure which one the invalid one was again. Talk about memory issues am I right?
If it's not already in, something you could do is highlight why that file was a mimic. Show which part of it was incorrect when it says it's invalid, and then replace it with another file, just keep that guy you got wrong and put it at the bottom of some list you have going on with all the other ones. That way, the player gets trained on spotting typical mimic traits. I'm spitballin' and nitpicking tho, so do keep that in mind : P