How is editing an existing Blueprint Interface supposed to work?

I created a blueprint interface with one function (call it FunA.)
I then implemented this interface in two separate blueprint components.
I could compile, build, run, no problem.
I then edited this interface to add another function (call it FunB.)
I saved and compiled the interface.
Surprisingly, I can still compile the blueprints that use this interface, even though I have not updated them to include this function.
I can also build the entire project and run it. (Nothing’s calling the new function yet.)

Now, even more interesting, I cannot add a function called FunB to the implementing blueprint – I get an error saying that name is already in use by another variable/function, even though I haven’t implemented it, and it doesn’t show up in the Graph functions browser.

So, two questions:

  1. Is there some kind of error checking that verifies that each blueprint that implements an interface actually implements all the functions of that interface?

  2. I see FunA in the “interfaces” section of the Graph pane of my implementing blueprints. However, I do not see FunB in that section. How should I go about actually adding this interface function to the implementing blueprint?

Wow, zero comments in three days. This seems like a bug to me. Is it known?

It is working fine for me on 4.2.1. Could it be that your FunB does not have any return values? In that case a function is not listed as an actual function but is available as an event in the Eventgraph. The name would still be in use though.
As far as I understand functions are implemented automatically. They will just not do anything if you keep them empty.