I don't understand why, but it's a common misconception that operators return their left-hand argument. Why you expect the following to print 3?

print( 3 + 4 );
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Then why would expect the following to print $text?

print( $text =~ s/this/that/ );
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Well wrong example, IMHO the misconception is motivated by

print( $num = 3 + 4 );
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which prints 7!

Occasionally it's a trap for me, too! 8)

IIRC the binding operator =~ will be changed in Perl6, which thankfully avoids this misleading association!