Workflow:
I've got a card in the collection "Skyreader Saves" - because I saved the article in Skyreader.
I go to 'update' on the card.
In the dialog I add the card the card to another collection, and I unselect the 'Skyreader Saves' collection, because I no longer want it to 'live' there - I've processed it!
I save and get the message "Error Could not update card".
The card is now in both collections.
thanks for the report. This likely has something to do with the way we handle the margin interop (looks like your skyreader saves are being saved under the margin lexicon). We will look into this and hopefully fix soon!