multicam editing: sometimes can't switch angle?

I have a multicam track that has 2 video plus 3 audio tracks. It is an interview and the 3 audio tracks are mics for the three people in the interview. The audio that links with the video are not used; other than for sync purpose.
So what I have is
angle 1: HD camcorder #1
angle 2: 4K camcorder #2
angle 3: lav mic 1
angle 4: lav mic 2
angle 5: lav mic 3
While choosing the angle, sometimes merely clicking on the angle in in the left monitor switches the angle. Sometimes I have to alt-click, and sometimes neither click would switch the angle. Pressing the numeric keys also doesn't do anything. I'm trying to switch audio from angle 3 to 4.
I'm a newbie and this is the first time I use this feature. What is the most likely mistake I'm making?
free version 15.1.1.005
windows 8.1
i7-4790k
32GB ram
Nvidia GeForce GTX 650
So what I have is
angle 1: HD camcorder #1
angle 2: 4K camcorder #2
angle 3: lav mic 1
angle 4: lav mic 2
angle 5: lav mic 3
While choosing the angle, sometimes merely clicking on the angle in in the left monitor switches the angle. Sometimes I have to alt-click, and sometimes neither click would switch the angle. Pressing the numeric keys also doesn't do anything. I'm trying to switch audio from angle 3 to 4.
I'm a newbie and this is the first time I use this feature. What is the most likely mistake I'm making?
free version 15.1.1.005
windows 8.1
i7-4790k
32GB ram
Nvidia GeForce GTX 650