In recent weeks I've begun to experience a problem: although I have multiple lists set to "continue adding," nothing new is being added and the (+) button to add more items is greyed out. This usually occurs when the "items to review" counter is in the single digits: all I get is really old vocabulary being repeated to me, and nothing new is being added. Stoping and starting adding from the various lists doesn't do anything, and I've already put "add speed" to high. Is there anything I can do, as this is really hindering my learning speed.

If you look at the study navigation page:

http://www.skritter.com/study

It looks like you're don't have any lists in the "Adding Words From" state. You can restart adding on your Integrated Chinese or CUHK Kung Fu lists and then you should be able to get some new words.

Actually, this problem was occuring when I had them set to add. The issue was that somehow the "Adding From" selector had switched to a completed section of the Integrated Chinese book after said section had been updated, even though I didn't tell it to, so there was nothing to add, but because the next section was also finished the program didn't know what to do and just did nothing although it didn't move to "Finished Adding." Perhaps this was a unique occurance in my case, but it looks like a bug.