Internal DNS on server 2008

I was having a problem with the host names for a couple of lab computers resolving to the wrong ip address. We have DNS running on a windows2008 DC with backup DNS running on another Server2008 box which hosts our exchange server.

I found incorrect ip addresses for the machines in question within the A records in the DNS on the DC. I deleted the records and that seems to have resolved the problem. I don't understand DNS in the windows world and have two questions:

1. When and how are the A records created for the worstations and why would they not be updated if the ipchanges?

2. The backup DNS shows all the records as being static. Is this OK? I assumed it had to do with it's role as a backup DNS and that it's records could only be changed if the primary DNS changed.

Any thoughts about what is/was going on would be appreciated.