I was wondering when someone will complain about that :). Previously the the "limit display" was independent to what was available - you had a choice of 0 (all) to 20. However, I was then asked to limit it to the maximum of what was available, and that is what it is now. i.e. you can only set it to as high as the max generation that has been loaded. The down side of doing as you requested (i.e. limit it to the max requested value), is that should someone request, say 15 generations, but there are only, say 8 available, then they might get confused by the fact that only 9 generations are being shown. As things are now, if you do not want to have to do the extra select and redraw, set the "limit display" value to "All" and then get whatever number of generations you want. The full tree will then be drawn.
I do agree that the current behaviour is slightly annoying, but I also don't quite know what the correct behaviour should be. Maybe others can chime in here and give their opinion?
Thank you for your feedback.