in reply to Re^2: Inconsistent captures in %+ and %-
in thread Inconsistent captures in %+ and %-

It must have been a bug which was subsequently fixed. I can reproduce your results with: 
This is perl, v5.10.0 built for x86_64-linux

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but not with: 
This is perl 5, version 12, subversion 0 (v5.12.0) built for x86_64-li
+nux

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