Sound mods broken for character voices?

I haven't paid too much attention to this problem until recently, where I've found that now none of my character voice mods are working if I'm playing on an sv_pure 0 server, whether online or offline.

Oddly enough, all other sound mods work just fine.

Here's what's working:

/sound/items
/sound/misc
/sound/player
/sound/weapons

And here's what's not working:

/sound/vo

What I haven't tested (because I don't use it):

/sound/ui

I've verified I've done this:

* All sounds are saved as .wav files using Audacity, sample rate set @ 44100 Hz
* Saved as both files with the appropriate sound folders under:

C:\Program Files (x86)\Steam\SteamApps\common\Team Fortress 2\tf\custom\nameofcustomfolder\sound,

Or as a VPK file in C:\Program Files (x86)\Steam\SteamApps\common\Team Fortress 2\tf\custom\ (FYI, I have no other custom directories or VPK files in use.)

I've checked the Console logs for any error messages that might suggest that the bitrate of the .wav files might not be usable within TF2, but the Console checks clean regarding sound file usage.

Any ideas, or is it the norm now to not allow voice file mods? :(

Thanks! :)

Sound mods broken for character voices?