Thank you very much: the gwt.codesvr was actually lost in one of the redirection used in the authentication process. I never even thought of it (thing is, just now I learn its purpose)!!!
Regarding compilation, I was aware of the double arrows, but they don't work if I don't recompile the code (in that case they're useless anyway).
In case others need it, I reduces the compile time by specifying to compile just for Chrome/Safari, by adding in the module .gwt.xml the folloing tag:
<set-property name="user.agent" value="safari" />