I did not see you subscribed, but I just closed the issue as we have found a solution. We will get you a build in the next few days that contains this fix. However in the meantime i believe you should be able to use this workaround:
<Expression ExternalProperty="TransactionOption">
<![CDATA[@[$Project::TransactionEnabled] ? 2 : 0]]>
</Expression>
Sorry that we did not get this work around to you sooner.