I just noticed that v1.28.2.55 introduced a minor bug, which breaks the MAC address saving introduced in v1.28.2.54 (causing the viewer to behave like it did before this latter release).
If you compile the viewer yourself, you may fix this bug by simply changing line 1115 of linden/indra/newview/llappviewer.cpp to read:
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| Code: gSavedSettings.setString("SerialNumberHash", md5serial); | |
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This will of course be fixed in next release as well.