This could have been the same issue as the "randomly saving huge EXRs" one. If that's the case, that would be a 3ds Max issue, where the values specified in the "save file" dialog are stored per-computer rather than per-scene. As we currently understand it, this is currently by design in 3ds Max.
Same thing will happen if you specify to save your file with 100% JPG quality, and then render it on another computer, where this is set to 90% - you will get a lower quality JPG.