The document for Subsuperscript says that:
To enter a subsuperscript in a notebook, use either Ctrl+_ to begin a regular subscript or Ctrl+^ to begin a regular superscript. After typing the first script, use Ctrl+% to move to the opposite script position. Ctrl+Space moves out of the subscript or superscript position.
This just create a expresion that looks like a symbol with subsuperscript! Specifically, I typed Ctrl+- / Ctrl+6 and a regular subscript / superscript appeared, Ctrl+5 and the opposite script appeared, and after I moved the cursor out of the symbol by pressing → and checked its
InputForm, what I saw is not something like
Subsuperscript[a, x, y]
What's wrong with it, I misunderstood the document? I use Mathematica 8.0.4 and Windows Vista Home Basic 32bit.