My S9Y saved any received pingback no matter if it was there already. As I thought this would be the case because I was testing WP pingbacks that days I fixed it for pingbacks already.
Since some days I notice that I get double trackbacks saved, too, and I was sure, that that never was the case before.
Now I noticed what's the reason of this problem: I switched off the standard anti spam plugin and exchanged it with the Bayes plugin. The standard plugin has an algorithm for denying double comments. I guess that's the reason, why I never get trackbacks saved twice coming in again.
I think this check should be part of the core, not of an anti spam plugin, because denying double trackbacks is not optional (handled by a plugin) but is nonsense always. And they are very easy to identify.
So I think, the check should be added to the core for trackbacks the same way I did that already for pingbacks.
Last edited by blog.brockha.us
on Sat Jan 21, 2012 8:04 pm, edited 1 time in total.