If an attribute is locally modified, e.g. @type on <abbr>, and is also modified in a user-defined ODD (e.g. with an <attDef mode="delete">, then the user-supplied modification is seemingly ignored by current ODD processing.
A very palpable bug indeed. The delete in the ODD removed the change mode stanza in the source, so the type attribute reappeared from the class. Nearly fixed, after a surprising amount of staring at gibberish XSLT and finding a separate error.
odd2odd xsl now tinkered with to support this. example in test21.odd