Comment 1 for bug 786391

Actually, I am getting to the bottom of this. The problem isn't with the build script. It's with the generation of the login URLs (and all the other URLs as well).

Note that when you start the server, you are linked to:
http://127.0.0.1:8888/Mugle.html?gwt.codesvr=127.0.0.1:9997
and it works without running ant.

But the URL for the login page is:
http://127.0.0.1:8080/_ah/login?continue=http%3A%2F%2F127.0.0.1%3A8080%2F
note that the continue= is set to redirect back to http://127.0.0.1:8080, without the ?gwt.codesvr... When you come back from logging in, you find yourself at:
http://127.0.0.1:8080/
which doesn't work unless you have recently run gwtc. If you manually put ?gwt.codesvr=127.0.0.1:9997 on the end of this URL, it works again.

But even if we fixed that, I would be worried that all of the Ajax URLs are losing the ?gwt.codesvr=127.0.0.1:9997 part as well, and therefore will require gwtc; though it doesn't look that way in practice.

Therefore, I guess for now a workaround is to keep sticking that annoying string on the end of your URLs, and then you can use ant devmode without ant. For now, I am de-assigning myself since this is NOT a build problem.