?> doesn't show when posted at the end of [code=php]

The closing PHP tag doesn't appear to be displaying when posted by itself inside of

[code=php][/code]

.

For example, regular code tags work fine:

[code]?>[/code]

However, PHP code tags don't:

[code=php]?>[/code]

When a user submits this, the ?> is removed from the code box, resulting in a blank code box being posted:

Tested on the phpBB.com Support Forum and localhost (Running 3.0.7).