dangoThanks yttrium for suggesting yayahud (which works), which made me realize the solution.
I'm gunna totally pass it off as knowing about case sensitivity in UNIX-like filesystems. Yesyes.
On a serious note, case sensitivity is definitely an important thing, but it's only one of the dozens of things you need to know as a HUD maker when trying to target non-Windows clients. I think the best thing to do is save this lesson in a folder and publish it, along with a bunch of other thoroughly-tested cases, in a "Targeting OS X and Linux with HUDs" thread later on, that way every HUD developer can easily read that thread and make their HUDs 100% compatible. For instance, iirc TF2 on Linux doesn't properly read TTF font files, they have to be formatted as OTF (not to mention that when defining them in ClientScheme.res you have to do so case-sensitively). Just one of the many lesser-known things you have to keep in mind as a developer.
dangoI don't think this was the case before MyM and I assume it's a bug
Wasn't the case before MyM because info.vdf didn't exist - MyM is what introduced the whole concept of HUD versioning.
Not really a bug so much as an unintended feature. Case sensitivity is something you have to account for on UNIX and UNIX-like filesystems, which Windows does not abide by. Frankly all this means is that Valve is actually doing their Linux programming correctly - TF2 really isn't running under a WINE compatibility layer. If they wanted to try and fix this "bug" they would actually have to develop a workaround that makes Source on Linux not conform to the Linux filesystem standard.