I was trying out the 1.9 testing version, and observed the following strange behaviour: I was repeating cards, and editing some of the cards as I was doing this. For one card, after I edited it during revision, it was shown again, and then a third time, before Pauker moved to another card. After revising all expired cards, I checked, and the card really exists only once. The really strange thing was that this one card ended up in batch number 9. The card was in batch number 6 and should have moved to batch number 7; I don't yet have a batch number 9 in this lesson (not for another year or so). What is also strange is that this happened to only one card, although I also edited others.
I have no idea if this is relevant, my settings for revising cards are to draw at random, and put the cards to the top in case of failure, and I repeat this lesson by remembering cards (not typing). This is on Windows XP, with all the patches (SP3) and the current version of Java. I have checked the lesson afterward, and everything appears to be fine. The lesson I was using is not the biggest lesson I have (thinking of memory limits, since this computer is some 5 years old).