From observing my own kids, I would say that difficult behavior (which can include tantrums) often precedes a developmental leap.
My husband and I have seen our DS4 go through this cycle three or four times in the past. Tantrums haven't been a huge problem, but many of our son's most obvious developmental leaps have been preceded by a phase when he had absolutely no tolerance for the slightest frustration and would cry at the drop of a hat. The first couple of times, it got to the point where we felt totally exasperated and inadequate as parents, but now we take it with a grain of salt and wonder what big leap is around the corner.
