Dar/bardar occasionally has some oddities.
I haven't seen it for a while, but I can remember nights within the last year or so where the arena had a buttload of people in it. Squaddies that were a sector over were seeing dots on dar that I wasn't, and squaddies that had been in the air for a long time didn't show up on dar at all until I got within visibility range of them.
There seem to be some pretty arcane factors that influence how often your system updates dar and what it updates.
Wiley.