[SamPlay]

Hi,
Half-life does not handle collision the same way than Quake.
It is POINT based, and move computations -like traces- are at least partly performed in hull-specific clip-bsp trees , which are basically pre-computed "hull-based inflated " worlds ( called "configuration spaces" in robot path planning; see zhlt code for details).
If the way recast computes contours away from walls is different than the bsp builder inflation/bevelling method, it may be closer in some occasions; to me, all this is the most obvious explanation for your bots unexpectedly bumping into the visible world.
I hope this helps.