Back door please!!

Today (and I think for the last couple of weeks) I noticed that the back door of the new buses - the ones without seats - almost always fail to open for passengers when the bus stops, requiring them to yell "Back door please!" in various intonations of irritation.

Normally, when a bus stops at a requested stop, the back door unlocks and is ready for passengers to step down on the first step or push to door handle, as the case may be, to open the back door and let them out. There is usually a very short pause between the bus stopping and the door unlocking, some kind of safety interlock but on the new buses, like the one I rode back from UBC today, at least half of the time the door did not unlock and passengers had to call to the driver to open the back door, which he did manually.

Is this a design flaw, bug or are our new buses breaking down already?

Now do I have to much time on my hands or what?