After having several guns, loaded and not, pointed at me from people loading at the back tables, I will never go back. I came back in after packing up (firearms on the line, bring cases to the firearms and keep downrange until cased), told them about the issue. Only response from an old guy from behind the counter, (paraphrased) "As long as they aren't loaded, I don't really care." I put my visit card on the counter (with two punches left), said I would not need it again, and left.
I've worked at ranges, and been to a myriad of them. I've been to places where they allow you to take your firearms to back tables. But I've yet to go to a place that had people loading magazines into guns at the back table and the people watching the place have disregard for it.
The various times I've been there, I have yet to see an RO on the line, just two guys behind the counter, swapping stories, not even occasionally glancing at the monitor. Guess I was there at the wrong times.
On my most recent visit (30 December 2015), there were signs along the back wall, indicating that firearms were not to be loaded at the rear tables, and could only be loaded on the firing line.
The posted range rules seem to support this prohibition, as well:
Range Rules | Parabellum Indoor Shooting Range & Training Center in Avon, Indiana