I ran some additional tests to what I showed in the OP and in Re^2: shebang problem on openSUSE:

ken@ibm-laptop:~/tmp> /usr/bin/env perl -e 'print "Hello, world!"'
Hello, world!ken@ibm-laptop:~/tmp>
[download]

ken@ibm-laptop:~/tmp> /usr/bin/env perl -le 'print "Hello, world!"'
Hello, world!
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ken@ibm-laptop:~/tmp> which env
/usr/bin/env
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ken@ibm-laptop:~/tmp> env perl -e 'print "Hello, world!"'
Hello, world!ken@ibm-laptop:~/tmp>
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ken@ibm-laptop:~/tmp> env perl -le 'print "Hello, world!"'
Hello, world!
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ken@ibm-laptop:~/tmp> env perl -l -e 'print "Hello, world!"'
Hello, world!
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ken@ibm-laptop:~/tmp> env perl -e 1
ken@ibm-laptop:~/tmp>
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This all suggests that env is parsing its arguments correctly. While it doesn't provide an answer to the shebang issue I'm experiencing, it does perhaps narrow down the causes.