I think this same combat lag is the same problem what I also experience with metallurgy. When I melt melted gold ores into ingots and back for some time, lag is increasing, starting at the change of item state (model) as little bit noticeable freeze moment. Whole game is frozen, including mouse cursor. With time the freeze length increases, so different freezes are just as one, starting with first changing slot ending with last. To add more info to the same, with time, my RAM usage increases, so I suspect some memory leak or some object not destroyed and staying in memory.
System is Debian Squeeze (Testing) 32bit, AMDx2 processor and graphics. The same is on another Windows XP, though cannot say anything about memory usage there.