17GB of storage space unaccounted for!

On both my iPad and iPhone, I watch my storage like a hawk. (Settings, General, Storage)

I upgraded to iOS 7 the day it came out on both iPad 3 and iPhone 4S. Mostly no problems whatsoever since then.

Tonight I had a big problem with Netflix...it just wouldn't work anymore (iOS app, not browser); so I deleted it (as a test).

Then I noticed that my 64GB iPad 3 says STORAGE: 21.5GB Available; 35.5GB Used.

This is completely inaccurate. I expanded the menu below, typed out the list of my 93 apps in a Numbers spreadsheet as well as their storage footprints, and added it up. It comes to about 17GB, NOT 35.5GB.

Does anyone have any idea what is going on here? Whether this is an iOS 7 caching or data ghosting issue? My iPhone 4S does NOT have the problem; storage figures are totally accurate.

On my iPad, I run the app Sys Status, and it's ALSO reporting "35.5GB used."

Help greatly appreciated on this! (Apple thinks I'm crazy.) I have of course rebooted 5x at least. I've also ended task on all open apps and powered down completely, let iPad sit for 5-10 mins, then turned it back on; I did this at least 3x. Same problem.

Fox, I think you're onto something—thanks! I *know* my iPad has music on it from my iTunes Match cloud....even though under Settings, General, Storage, Music it says "No Data"! I've tried in vain to delete the music by turning off iCloud Match, logging out of the iTunes Store, etc., but nothing works. There's a "shadow" copy of my Match Music stuck on my iPad that I can't delete.

You know, I wish I *could* hook up my iPad to one of my Macs to sync. But they're both too old for that. I've done all my iPad syncing over wifi and the cloud for years because of this.

So I'll probably have to Reset All and Delete All Content unless someone else has a suggestion this morning.

I just blew away ALL my iPad settings and data...now I'm setting it up from scratch.

I haven't had this much fun in months.