Because if it would simply append, chaotic/confusing and wrong logs will be created....
You could talk to the same person with both your .NET accounts and both .NET accounts can be different persons. Both of the .NET accounts will have their convo mixed up with the contact if it was "appended".
Furthermore, logs aren't save line per line but after a certain timeinterval.
The above would all contribute to malformed logs if they were appended. In short, there is nothing abnormal about it, in fact it is very logic that it is NOT appended...
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