This is the official response I just received from US on my US-plated RGN-PEK-FRA-PHL-YUL ticket. They say the DOT rule on price increases only applies if travel originates or terminates in the US, not if there's a connection in the US of less than 24 hours. I still haven't heard back from the DOT on this though:

Dear KevininRI:

Thank you for writing to US. I’m happy to have the chance to respond to your concerns regarding your tickets purchased through Travelocity from RGN to YUL.

According to our research, the International Air Transport Association (IATA) erroneously filed a significantly under-priced fare from Yangon (RGN) to Montreal (YUL). These were made available on third party travel agencies and a number of purchased fares were ticketed on US Airways ticket stock, as well as other airlines.

Although your ticket was booked on US Airways ticket stock, US Airways was not the originating carrier and therefore, was not the first carrier to cancel travel. Your ticket originated on Air China and they have also cancelled travel. Since this was your originating carrier you would not have been transported to Frankfurt in order to use the US Airways segment(s).

In Addition, the US Airways Legal Department has communicated with the Department of Transportation Legal Department and was informed, as a matter of enforcement discretion, The Department of Transportation would not apply the rule on post-purchase price increases where the ticket does not originate or terminate in the U.S. and all layovers in the U.S. were less than 24 hours.

I understand that this was a frustrating situation and I am sorry if it has created any difficulties for you. After reviewing your ticket I see that Travelocity has now refunded your ticket. If you have any questions regarding this refund, please contact Travelocity directly.

We value your business and are working hard to earn your continued patronage. We hope you will give us the opportunity to do so.

Sincerely,

xxx
Customer Relations
US Airways Corporate Office