I have noticed there were some updates to the stable version, where I thought that this has been fixed now. It's quite strange, but in short, this isn't properly fixed. I have tested the development version as well, and it's the same there, the bug with duplicated contacts in Jabber is not fixed (Edit: I'm still figuring out how to reproduce it in a reliable way). At the same time while I tested it, I have even noticed a second bug where Miranda NG crashes when I delete a new contact (with a fresh Jabber account without any contacts). I think I'm going to open two tickets about this and will link them here or in the bug reports section when I'm done.