OK, more info on this. There are two possible function parameter tooltips displayed. One which starts e.g. [1 of 2], and the Ctrl-page up/down works OK in this one.
The other has two little up and down arrows, and works differently (i.e. ctrl-page up/down doesn't work.)
Dual tooltips will fixed in 1230. The Control-page up/down does not work with VS.NET's tooltips, only VA's. To enable VA's, you will need to disable VS.NET's in the Tools/Options/Editor/C++.