Subgroup wrong when matching (.)(?=(.)) against "XY"?

The following case behaves as I would expect:
   Perl5 Expression: (.)(?=(.))(.)
   Search Input: XYZ
   Match 1: XY
      Subgroups:
         1: X
         2: Y
         3: Y

But the slightly simpler case, below, doesn't seem to match the 2nd subgroup
correctly:
   Perl5 Expression: (.)(?=(.))
   Search Input: XY
   Match 1: X
      Subgroups:
         1: X
         2:

Shouldn't the second subgroup in the second case be "Y" instead of blank?
I'm trying this in the "Demonstration Applet" from version 2.0.6.

Adrian