Hey Steve
The prinicple is this:
You sign into a teamwork file and save a draft locally. For example, if the PLP is on the server, you sign into it, and save a draft to your computer's hard drive. Once you have saved the draft, you can copy it, either in the operating system, or within ArchiCAD, using Save As. You are then free to make various design changes in any of the drafts. When you have decided on a final design, you send the changes from that draft back to the main model (the PLP). You will be warned that the draft has a different ID, but consider that a good thing rather than a bad thing and proceed. Once sent you are free to sign out of the project altogether.
I am not sure what happened in your case, maybe someone (the Administrator) forced you out? If you really want your latest information to be included in the main model, you may have to sign again, save a draft, (optionally copy that draft), and copy & paste the information into it, then send the changes back to the PLP.
I hope that helps. I'll be in the UK next month, let me know if you'd like to get together.
Cheers,
Link.