CS0309: constraint has been violated. (possible bug?)

Does anyone know why the following doesn't work?

interface B is derrived from interface A, and should contain an implicit conversion from B to A
error CS0309: The type 'constraint_bug.interface_b<T>' must be convertible to 'constraint_bug.interface_a<constraint_bug.interface_b<T>>'
in order to use it as parameter 'T' in the generic type or method 'constraint_bug.do_something<T>(T)'

class constraint_bug { interface interface_a<T> { T some_func(); } interface interface_b<T> : interface_a<T> where T : interface_b<T> { void another_func(); } staticvoid do_something<T>(T val) where T : interface_a<T> { val.some_func(); } staticvoid do_another_thing<T>(interface_b<T> val) { do_something(val);// CS0309 (seems like a bug). } }

adding interface_a<interface_b<T>> as a constraint doesn't help.

[1479 byte] By [JoeR] at [2008-2-26]