[Windows Central Question]

Any text message received or sent on/by the Windows M8 is also duplicated on the Lumia device but not vice versa.

When I receive a text message on the M8, a duplicate copy is also received by the Lumia.

Similarly, when I send a text message from the M8, it would also be reflected on the Lumia that message was sent. In both cases, it does not happen vice versa (Lumia to M8).

Both devcies has the same Microsoft Account.

[Harrie-S]

Then on your Lumia you enabled in settings > backup > text messages backup.
And on your M8 you did not enable it.
Because you use the same MS account you are able to "see" text messages on all your phone with the same account, if you enable "text messages backup" and it does not matter if the phones have different numbers.

So if you do not want them "duplicated" switch off the backup.

[mhooks]

Try these steps: Settings, applications (along top ribbon), phone, international assist - slide to the off position. This corrected my issue.