This is common and happens to everyone. Maps do not refresh over the entire zone constantly or you would not be able to play eq no mater how much ram/graphics card you have in your pc.
I forgot the exact range, but there is a exact range that is always updated (I think 500 units + your group itself is constantly updated) anything else refreshes over a certain period of time and I never bothered to know how long that was so cant tell you that length.