Unexpected error in covering effects under owner regions

[reprogrammer]

I don't understand why dpjc reports the following error message.

Effect summary does not cover [invokes <>m2(C<P3>) with [writes P3 : * : [?] : *]]
C.java:2: bad effect summary
    public <region P2>void m1()
                           ^
1 error

class C<region P1> {
    public <region P2>void m1()
    writes P2 : * {
            m2(new C<P2>());
    }

    private static <region P3>void m2(final C<P3> c)
    writes c : [?] : * {
    }
}

[reprogrammer]

Rob said the following on the mailing list.

Looks like a gap in region inference for method parameters. The region inference is brittle and not well specified. Basically, it works unless it doesn't. You can always work around this sort of thing by giving an explicit region argument: C<region P2>m2(new C<P2>());