> I just tried
>
>   M-x compile RET C-a C-k emacs -Q -daemon RET
>
> and that started a daemon which stayed up in the air and didn't exit
> or get killed.

Yeah, it also works here. I can only guess that Gradle daemon is terminated
if
stdout is closed before the main process is shut down or something like
that.

> If you see the same on your system, then Gradle,
> whatever that is, is indeed somehow involved in this, because without
> it everything works as you expected.

It's a pretty standard build tool (Make of sorts) in a Java world. They
will of
course tell me (for the second time, I already asked for support for this
problem
before) it's an Emacs' fault, because outside it Gradle works fine.

> Also, you didn't tell which version of Emacs you used (I used the
> latest development sources).

GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.9) of
2015-08-27,
a fairly recent trunk.

Paul