This is the result of the QW (queue weighting) system. This system is pretty complex and hard to understand, and its end results are harder yet to understand.

Here's how it works. All puzzles in the queue are assigned a queue weight number, which you can see right next to "approximate queue position" when looking at your own problem. If a single author has XX puzzles in the queue, the oldest two are assigned QW 1, the next two are QW 2, the next two are QW 3, and so forth. The queue is not arranged from oldest to newest, but rather first arranged by QW numbers. Effectively, only puzzles with QW 1 will show in the top 10. The QW numbers are calculated each night.

There are many results of the QW system, many of which are not immediately obvious. One result is that problems will sometimes disappear from the top 10 at midnight (in flooble time), because they are getting displaced by older problems that have just been newly calculated to have QW 1. These problems have simply been pushed temporarily past sight to number 11 or so.

Of course, this is not the primary, nor intended effect of the QW system. Mostly, it keeps the puzzles diverse; no one author will dominate the top ten. Also, it gives a slight advantage to those who only submit a few puzzles. I believe it even prevents to an extent submitting lots of blank problems, since having lots of problems in the queue only means that the ones in the back wait longer.