If it makes you feel any calmer, I'd say pretty much any breed of dog (and plenty of cats too!) can be unpredictable.
I certainly found the situation quite extraordinary one morning when I went out for a walk with my cat (yes, cat) and at one point, after we'd been through a grass area between two roads, she had run on ahead of me and then 'froze'. Once I got further up the road and didn't have cars blocking my view, I saw a chap with 4 dogs on leads, under 15 feet in front of my cat, who was just 'holding her ground' while waiting for me.
The bit which surprised and pleased me was that not one of the dogs barked or looked threatening, they were just standing still. As I got closer I congratulated their owner, expressing my surprise that they had not barked - it was a little before 8am on a Sunday, and the thought of 4 dogs barking their heads off at my cat was easy to imagine!
Anyway, my cat, once happy to know I was nearby, walked round the corner of the street, and glanced back once to see they were not following. Other times, coming close to a dog (or more likely, a barking dog) would get a more defensive attitude from her, tail full and sticking out or up, back arched and some hissing / whining, to point out she may be smaller, but she won't hold back if she is attacked!