If you are veginnig with altium : turn on the status bars. Both of them whenever you are doing something keep an eye there. Altium cycles messages like an rss feed showing you what key does what at this point in time.
Heh. Well, I was almost "ending" with Altium last night. I updated all the PCB footprints from a library and the f-ing thing rearranged half the components on my board. My previously beautiful PCB was splattered with green DRC blood from all the overlaps and open connection. WTF?
About half the components on the board got moved and/or rotated from the library update. Everything came from that library in the first place, and I have no idea how they got out of sync, or even why Altium would decide to change placement based on something in a footprint library. Anyway, I noticed that all the affected components had the "Flipped on Layer" bit set (whatever that means). Unflipping that bit and then repositioning the components made it happy again.
I'm sure there's some reasonable explanation for what the program did, but it's behavior (in that instance) was indistinguishable from a horrible data-losing bug.