Not sure if this is common with Cat 1 alarms, but i think mine is playing silly buggers.
When i first get in the car i dont have time to start the engine straight away (steering lock etc) so the immoboliser cuts in. When i put my keys in the ignition and turn the key it locks all my doors. I have to press the alarm button on the key fob to get past the immoboliser, but all my doors are still locked. I have to open my door which in turn, unlocks all the other doors.
However today it didn't unlock the back door (drivers side).

Any ideas?

 

I'm no expert but someone on SN has detailed instructions on enabling/disabling alarm functions using keypad - you may have inadvertantly reset something. However, if I read you correctly, it does sound more like strange random things are happening - maybe the battery is not in tip top condition or on the way out, as a dodgy battery makes the alarm do some odd things.

 

If one of the doors didn't open, it won't be anything to do with the alarm. The alarm simply sends out 1 signal to the cars central locking system and all the doors should unlock. If one doesn't, it could be that the motor in that door is getting old and maybe in need of lubrication or replacement.

Keep an eye on it.