I too have struggled with developing for PC with C3 + NWjs. Here's what I've learned about fullscreen that is not immediately obvious without some digging.
There are 2 ways to do full screen with NWjs (that game devs care about).
1) HTML5 API, which I believe C3 implements into it's "Request Fullscreen" action from the "Browser" object, which allows you to fullscreen a specific element and it's children within a web page. It comes along with all the security/user safety baggage.
2)The NWjs Window Object, which C3 does NOT implement into it's "NWjs" object, which I believe they should, but they haven't. This way uses the operating system function to fullscreen the entire window. No baggage with this one, it should work 100% of the time.
So in your bug ticket, since you're referring to the Browser request full screen action, Ashely is right, he can't do anything about how the browser implements the HTML5 API. Maybe NWjs made a change, or maybe chromium made a change, who knows.
There's just 2 lines of code you need to get access to the NWjs window object.
var ngui = require('nw.gui');
var nwin = ngui.Window.get();
Then another 2 to enter or leave fullscreen.
So insert that code into an event sheet, with an inline script, where ever you want it triggered. The image below is from the KiwiStory sample project that I slightly modified.
To configure how the fullscreen works (letterbox scale, etc), set that in "Fullscreen mode" in the project properties under "Display"
I hope that helps.