I'm using Autocad 2010, and have never had this problem before. Working in plan, the traced linework over 2 xref pdfs (both on locked layers) keeps moving in model space either when I'm performing another command on different linework or when I regen. The layers that keep moving are all locked, and do the same when they're frozen. There is no consistency to where they move--usually within the same screen view--so it makes me wonder whether I xrefed these files into a different plane? They're not georeferenced though.
Or is this just a bug? I thought the file may be corrupted so started a new one, still same issue. Suggestions?