I still have the HTML file from my query of the SSA database regarding the 2005 data, for building my own name database. This file is from October 21, 2006. At *that* day Ella was ranked 22 and Anna was 23. If you go to the SSA site *now* and query the 2005 data, the two names are reversed.
Unfortunately the data in the older file is without number of births, so I cannot check the revisement theory...
I checked the boy names: There you have a change even higher up in the data: Last October Ryan was given as 13, followed by David on 14. Now the order is reversed.
So, whatever is going on, the phenomenon is real and maybe quite frequent.