Maximum participants warning missing for paid events in CiviCRM back-end

On a client site and the demo site running 4.5.0 there is a problem whereby when you try to register a participant on a paid event (and it is already full - max participants is reached), there is no warning.

For free events (ones without a fee) the warning message shows up fine. I looked at the participants.php file and .tpl file but couldn't work out where it was failing. From what I could tell, the php file is sending the correct number of registered and maximum participants.

Appreciate some help on this, as it also affects latest version.
Jon-man