Gradle 1.8 is less forgiving for incorrect ivy.xml of the resolved dependencies. Missing namespace may lead to resolution errors:

//correct:
<artifact name="foo-src" type="source" ext="zip" conf="src" m:classifier="sources" />

//incorrect, 'classifier' missing a namespace:
<artifact name="foo-src" type="source" ext="zip" conf="src" classifier="sources" />

We probably won't take any action on this mild incompatibility (otherwise what's the point of xml validation?). The xml file should be corrected, instead. I'm creating this ticket for documentation purposes.