That's the reason I pretty much avoid mixed use paths. Pedestrians (and amateur cyclists for that matter) are totally unpredictable. You either need to ride too slow to get any kind of workout, or be on your toes the whole time. The type of behavoir you've encountered I've seen from both cyclists and pedestrians. It reminds me of back in my college days when I was riding on one of the streets near campus. I was doing maybe 25 mph and a student riding on my right decides to make a left turn. Of course I had no way of knowing this. She was moving rather slowly, like most of the students rode (I was one of the few who actually rode at more than jogging speed), so I was preparing to overtake her on the left side. After a few near misses I'd gotten in the habit of covering my brake when passing slower cyclists just in case. Sure enough, maybe about two car lengths before I'm on top of her she decides to cross two lanes of traffic without so much as a glance back. I hit the brake, can't swerve left as it would put me into oncoming traffic, and lock rear wheels with her. No damage to either bike as I'd slowed to a few mph before the collision. Man, I let her have it, mentioning what if I had been a truck or bus. I hope she learned her lesson.
Bottom line, any venue where you're more likely to encounter pedestrians or amateur riders is not pleasant. That includes mixed use paths and areas around many colleges. Oh, and I hope the encounter I described above isn't taken to mean that I look down on all female cyclists. Quite the contrary. I've encountered some great ones. Back in the mid 1990s I had a great ride on the 73rd Avenue bike path with a female rider right behind me. I was pushing myself right to my limit, averaging around 22 mph for over 3 miles, and she kept right on my tail the whole time, even up the hill near Utopia Parkway. And she wasn't close enough to catch my slipstream, either. To say I was impressed was an understatement. I did and still do drop most riders, even those half my age.