Workaround: change current Alexa Says/Custom action which is what triggers this bug right now, to Messaging/Send Announcement action. It generates an extraneous tone, but at least it doesn't pollute the voice part with this garbage.
That was me, might as well join the conversation directly. It sounds like Amazon is bracketing the actual Say text with something close to <AmazonForceUnitSelection> "actual text' </AmazonForceUnitSelection>. Anyone has Jeff's phone number?