Seems a bit of an odd move on the surface....
With Forster due back "possibly before the end of the year" and Steklenberg looking solid with the potential to convert his loan into a permanent move (?), plus the recent signing of "the next Joe Hart" (the lad from Shrewsbury), its difficult to see Gazza getting much first team or U21 action in the medium to longer term.
That said, based on recent performances (end of last season + the U21s + pre-season friendlies) he seems to have gained considerably in confidence, so maybe the plan is for him to be Forster's long term back-up after all, which would obviously squeeze Steklenberg out of the frame...