I've read something similar in the past regarding them POSSIBLY requiring your case for promotional purposes for a short period - I'll have a look tho and see if this stands this year too...
EDIT: It isn't specific about you sending them the case but.....
9. Reprint or use of your Case Mod and Case Mod images will be at our sole discretion and will occur without compensation to you.
10. We may use your Case Mod and Case Mod images with or without any pseudo (pen) name credit.
11. Our right to use your Case Mod and Case Mod images is perpetual and may be assigned by us.
12. We may use your Case Mod and Case Mod images locally, nationally or globally and such use may be made in any media, information or communication platform (including Internet advertising) currently in use or later developed.
All of those do infer possession - it's kinda hard to use something exclusively and perpetually without actually having possession of it.... The fact that they specifically state "your case" AND "Case Mod Images" is somewhat worrying.... Hell, rule 11 basically also says they can give it away to someone else entirely....