I recently subscribed to the ANRB Real Time feed.
Today I noticed that some of the aircraft that I could see on both ANRB's network and the PlanePlotter network (always in real time) were in different positions. They were a few miles in trail on ANRB of their current locations as shown on PP.
I run PP with position estimating turned off, so these aircraft are not simply continuing along an estimated line. They only "move" when the network updates (about every 60 seconds).
Below is a screenshot from each program, taken nearly simultaneously (a few seconds apart), with the out-of-position aircraft each marked with a letter for comparison.