I am not sure if this is my browser (currently using Chrome), but occasionally when i start typing a card and there is only 1 card matched, i can hit tab or enter and it will fill in the autocompleted card name, but sometimes it will re-match what was autocompleted and when i hit enter to submit the form, the last few characters of the matched card are added and then it says it won't match.

For example type "Clergy of the holy" then hit enter to autocomplete, then hit enter to add the card...but in this case it autocompletes the "Nimbus" a second time. Again this only happens occasionally but seems to happen more when i type quickly and hit enter very quickly.

I have this same thing happen. However it usually happens on my netbook when I am adding a bunch of cards. I think it has to do more with the speed of the PC and how fast you can type than the actual autocomplete feature.