Bafflingly, the U.S. models' biggest feature gap seems to be a software limitation.

For the past year, high-end Sony phones sold in the United States, in the Xperia Z5 and X series, have lacked the fingerprint scanner tech found in their international cousins — a major feature omission for a modern high-end phone. The same applies to the recently launched Xperia XZ and X Compact — fingerprint internationally, no fingerprint in the U.S.

Now it appears that the U.S. models' fingerprint sensors may merely be disabled in hardware. XperiaBlog has discovered that flashing UK firmware to a U.S. Xperia XZ results in a fully functional fingerprint sensor. The relatively simple flashing process is detailed over on XDA. With the UK firmware flashed, the fingerprint scanner works just like it would on an international Xperia XZ or X Compact.

The revelation only makes the lack of a functional fingerprint sensor in U.S. models appear more strange.

Android Central put the question of the missing fingerprint sensor to senior Sony representatives at the IFA tradeshow in Germany this August, but the company wasn't able to give a clear answer on why the U.S. models lacked such a key feature.

One possibility is that Sony didn't want to pay the licensing costs attached to fingerprint technology, and so chose to ship the same hardware as the global version, but disable the feature in software. Another is that some outstanding agreement with the U.S. carriers — back when Sony was selling to Verizon and T-Mobile — may not allow it to. We've reached out to Sony U.S. for comment on today's news, and we'll update this story with any response.

MORE: Sony Xperia XZ review