Yea, not a good idea...

So for Christmas this year, i got a pressure cooker and a cookbook.
I was really excited to use it.
I really thought it would make cooking quicker, allowing me to make better meals in shorter amounts of time, and thusly spending more time with the girls.
So today, i decided to try it out for the first time.
I definately should have done that on a weekend first.
I flipped through the cookbook and found a recipie that i thought we'd all love.
It was for Adult Macaroni and Cheese.
Basically, it's macaroni and cheese with white cheddar cheese, cream cheese, veggies and bacon.
So i followed all the instructions of the recipie to the letter, not missing a step, doing every single thing it said.
I got it all in the pressure cooker and closed it up.
I turned it on and started gathering all my stuff together for work.
Then, i heard the pressure cooker start to whistle.
Now, never having used one of these things, i had no idea whether this was a good or a bad thing.
So i got the instruction manual and started looking for an answer.
Nothing.
Wouldn't you think it would say SOMETHING about what's going on here?!
But as i was flipping through, i can across a section that said "You should not put rice or pasta into the pressure cooker"
I definately thought this was weird, because the cookbook that i got to go with the pressure cooker said it was perfectly fine to put the pasta in there.
As a matter of fact, they have an ENTIRE SECTION devoted to pasta recipies!
Well, as i'm reading this and becoming more and more confused, it started whistling louder.
I peeked my head around the corner just in time to see the thing explode.
Well, not like "BAM" into a thousand pieces explode, but something happened and all this steam rolled out of the top of it, and there was some sort of pasta water, i guess, all over the counter, the floor, the window, the cabinets, even the pile of stuff half way across the kitchen!
So needless to say, i was a bit late for work because i had to clean half my kitchen!
But when i opened the pressure cooker to see what had happened, everything seemed cooked!
It's so weird!
So after i cleaned up, i thought, what the hell! What worse could happen right now.
So i finished off the recipie like it told me too, lol.
I put the cheese and the toppings on, i stirred it a bit to mix it in, and then i closed it back up and put it on keep warm so Frank will have a hot meal when he gets home.
Now, there's no promising it'll be a good meal, lol.
So we may very well be eating McDonalds tonight.
And now i'm at work, googling, trying to figure out what went wrong with the darn thing.
Was it the pasta?
Was something not tight enough?
Did i set something up wrong?
I can't seem to find the answer, so if any of you have a clue, i'd love your help!