Why did the moon abruptly change positions in the sky?
Three or four weeks ago I was outside showing my neighbors how cool the moon was through a 'backyard' telescope in broad daylight (~8PM PDT). It was 3/4 of the way across the sky (setting behind the houses behind us.) Two weeks later the moon was not even up yet at 8PM. The planets I've been watching (Jupiter, Saturn, Mars) are all rising and setting a little earlier each day as I would expect.
Why did the moon abruptly change its position in the sky a couple of weeks ago?
I look at the moon every night, and it is behaving strangely. There have been a month or two where the moon has been completely full for 5 days. This month it has moved drastically, and you never know where it's going to be in the sky. I've been watching it every night.
Compared to the planets the moon changes it's rise and set times very quickly. Using the calculator on this page it can be seen that if one were looking at the sky on May 1st, 2014 from Irvine, California the moon set at 10:08PM (which at 8PM would have had the moon most of the way across the sky as noted in the question.)
The moon rises and sets approximately one hour later each day. So, by May 14th the moon did not even rise until nearly 8PM - which also correlates with the observations noted above.
Contrasting that with the other context point made in the OP, using this page we can see that on May 1st Saturn rose at 8:07PM and on May 14th rose at 7:11PM.
So while the moon changes its rise a set times by almost an hour each day, the planets change much more slowly by comparison, almost an hour over two weeks.
If one weren't continually watching the moon's progression it would appear to abruptly change positions when comparing it to the planets' movements.