Citation problems

Hey there,

I am using the reference manager since a few month.

Usually I cite sources of the same author and the same year in the text as follows:

Oliver 1999a, Oliver 1999b and so on.

In the last few month I had no problems with this kind of citation.

But since yesterday the Reference Manager uses this in-text-nummeration (a, b, c etc.) also bei sources with the same author but different years!

That means I have citations like this in my text: Oliver 1985a, Oliver 1999b.

Could you give me some feedback where the problem could be?

I am sure that I haven`t changed anything in my output style since yesterday.