The fix for this bug has been committed.

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Thank you for the report, and for helping us make PHP better.

there were a duplicated input with the same name as the superseded dropdown, and 
that overwrite the selection of the dropdown.
I've removed it, so after the code get synced it should work as intended.

ps: I've also debuged from the code, that there is an option to display a link for 
the superseded package, but for that to be displayed, you have to put pecl.php.net 
to the 'New home link' field.
You can see that in action on the classkit package.