This effect is well known with function arguments and any repeated variables , but IMHO not common with built-in operators.°

I consider this an implementation glitch which should be fixed if possible.

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

°) some take lvalues like substr but there is no reason to consider concat alike

Update

Changed splice to substr

In reply to Re^2: ${^POSTMATCH} problem by LanX
in thread ${^POSTMATCH} problem by pl_pm

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