I'm confused by the way masters work in CC 2015. In the past, I'd create a master "A" that has the main text flow for a book. I'd then create "B", which inherits the main text box from "A" and adds a footer, and "C", which inherits from "B" and adds a header.
When I create a new document in the latest version of CC 2015 with "primary text frame" enabled, it creates "A" with two linked text frames. Great. Then I create a new master, "B", as "based on master "A". There are two selectable text boxes already there in "B" (to my mind this is odd and they should be inherited and unchangeable without overriding from A). What's more, the left frame has the page icon "click to make this story the master's primary flow", while the right one has the icon saying "This story is the master's primary text flow". Why there's a difference between the two is beyond me – there isn't in the A frame. Am I doing something stupid or is this buggy?
Further to this, here's some screenshots of the – to me, bizarre – behaviour.
Step 1: New document, with "Primary Text Frame" enabled (I've moved the margins to make things clearer). What happens when I select all on the master:
Step 2: create new master, B, based on A. Selected all on the master spread to show what's where. The left page isn't part of the primary text flow, but the right one is. Both are selectable, neither need to be overridden from A, and they're no longer threaded.
Step 3: create new master, C, based on B. Selected all on the master spread – they're no longer threaded, and only the right-hand text-frame is selectable at all now; the left-hand side is dotted to suggest it can now be overridden.
I haven't done anything weird, just created C, based on B, and B, based on A. Why is this so random?!