4.0.0.0.beta1 Version + (Build ID: b0eb7231a9643d71be3125be7248c91242339ab
under Vista

Steps to reproduce:

Purpose: Conditional Formatting on cell A1 of Sheet1 with the following condition: $Sheet1$A$1^2>$Sheet2.$D$1

1/ Format > Conditional Formatting > Condition
2/ select the condition "Formula is"
3/ position the cursor in the input box
4/ click cell A1: the input box contains: $Sheet1.$A$1
5/ with the keyboard, add  ^2>  to obtain: $Sheet1.$A$1^2> (leave the cursor remaining after >)
6a/ it is impossible to select Sheet2
6b/ so we try now to work on Sheet1: select cell D1, the input box now contains: $Sheet1.$A$1, the previous content is erased. We expected: $Sheet1$A$1^2>$Sheet1.$D$1

Points 6a and 6b worked correctly with versions 3.5 and earlier.
Confirmed on the French en-qa list