Hm, weird. I've definitely got a list.
Well, I've only got the "default" list (I use it for keeping track of new stuff that I want to read). I selected an item and then click on the reading list button and select "Move to list". This usually just adds it.
The last one I added was (according to the list) on 16th December, before I upgraded to 0.9.12 (but after, it looks like maybe, 0.9.10).
Should I uninstall and reinstall do you think? I've only got 15 items in the single list.