If two types P and Q are derived by extension (perhaps indirectly) from the base type B, and if they both introduce new element particles named N but with different incompatible types Y and Z, then the schema processor wrongly reports the schema as invalid, with an error such as
The type P is derived by extension, and reintroduces element N which was defined in the content model of the ancestor type B with an incompatible type. Type Y is not validly derived from type Z.
A patch is being placed in Subversion. Note that the patch changes an interface between Saxon-B and Saxon-SA code so it should not be applied by users who do not have access to Saxon-SA source code.
The problem affects older releases but the patch is being produced for 9.1 only.