Similar Problem over here.
Job is rendering, Deadline grabs new task, frames are rendered fine and written to hdd, but tasks status isn´t changed to complete.
So I have a job with 220 frames. The first 120 tasks are rendered so far, but in monitor the first 5 tasks of this job are still marked: rendering, while the others status´ is set to queued altough the job is already 50% done.
Furthermore it takes a very long time till the slave grabs the next task (even if status isnt updated in monitor and frame is already written out)
Right now I check if the frame is written and set the status to complete by hand…this is no long term option 
Problem just occurs with Vray Job (directly from within maya2011 SP1 and not submitted via vray standalone)
Mental Ray Jobs work as intended.
Maybe it´s due to the scene? It´s a very heavy scene with lots of vray proxies (about 64Million Polys, estimated usage of ram about 4-5GB)?
In another layer from this scene where the proxies were hidden the problem didn´t occur.