Not sure if it's relevant, but I've noticed that when in bootloader->fastboot, whether the USB is already plugged in when entering fastboot or I connect it after, the "fastboot" status at the top of the screen doesn't change to "fastboot usb" unless I use the volume buttons to scroll through the menu options.
Also, when HTC Sync Manager is not installed, every time I connect the phone to the computer via USB I repeatedly get pop-up messages asking to install HTC Sync Manager, but then of course when I do have it installed it attempts to open every time the phone is connected and begins searching for media to import; it's driving me crazy.
My current setup is simply a stock T-Mobile 4.1.2 CWM restore (with all the T-Mobile bloatware and everything), with ClockworkMod Touch Recovery flashed (not merely booted to) and superuser.zip flashed.
ADB commands work, fastboot commands return absolutely nothing. I can also navigate to the Internal Storage through Windows Explorer and copy, move, and delete files to and from the phone when it's connected via USB while booted. All ADB, fastboot, SDK, etc files have not been touched (as in, everything worked fine a few days ago, and no changes have been made to any such files or locations since then) and still remain in the C:\HTC One directory.