You state: "The 1099-R from my former employer says that all the dividends from the Roth 401K were taxable." If the "dividends" you refer to are the amount of 401(k) "after tax" money rolled into a Roth account in the same 401(k) plan -MINUS- your basis (the "after tax" amount you contributed), then the 1099-R taxable amount looks to be correct. The above "after tax" contributions to a traditional (non-Roth) 401(k) are non-taxable when rolled over to a Roth account in the same 401(k) plan, whereas any growth in the "after tax" account will become taxable at roll over.
