Just some information from my personal experience:
(when I talk about "visually saved" meaning in the raid info tab)
I did a Firelands after clearing it before.
- I server transferred in Firelands and when on my new server I was not saved to anything at all.
- I server transferred in Dragon Soul and when on my new server I was visually saved to all the same raids.
However I COULD do Karazhan however it prompted me that it would save me to a 0/12 (or what have you) instance and I could rekill Attumen again in that week. In raid info it said I was saved.
I could also do a new LFR and was able to roll on items.
I also got a reset on VP.
I TRIED to do a BH and I was saved and it would not let me kill Alizabal again. I invited some random to raid and checked for myself that I was saved.
I DID NOT attempt to do a Dragon Soul after seeing I was saved to BH.
I may have just had a freak occurrence however I am tempted to believe after all the hype about guild's server xfering for more gear etc they changed it, at least for T13 raids/bosses.
Any other info on the matter?