If a PUBLISH request is sent before a 200 OK for the previous PUBLISH request is received, the E-Tag is reset which leads to inconsistent presentity data in the presence server.
This is happening because the second PUBLISH is sent with the same E-Tag as the previous one, but the presence server has an updated the E-Tag (generated while handling the first PUBLISH).
The pua module should implement a queuing mechanism for subsequent PUBLISH request while a previous PUBLISH transaction is in progress. No new PUBLISH requests should be sent before a response to the previous PUBLISH request was received and the E-Tag updated.

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