that has been happening to me on and off for a few months, on many of the computers i use infrequently, I think it is a cookie thing causing it to not be remembered that those achievements have ALL been obtained by me years ago.
Erika on the other hand says it is a code bug introduced when they added the over e308 things. But for the life of me I do not know how a company who knows this has been the case for months and who have had DOZENS of new things added to the code since then, has specifically NOT spent a second to fix the issue.