I had this exact same problem less than a few days ago and the way to resolve this issue (well it worked for me) is to do the following.
- With Safari open click the Safari tab to show the option of reset Safari.
- Click on reset Safari and then your be displayed with a window that askes if you "Are sure you want to reset Safari?"
- Before reseting Safari you may want to uncheck some of the boxes, I unchecked the reset top sites and my auto fill form text.
- when you are happy with your unchecked or checked selection then click the Reset button.
- Safari will reset its self and reopen a fresh.
- You should now be all fixed.
I closed Safari at this stage and then reoped it and my reading list was fixed and still all my reading items where as I left them before I had the problem.
Hope this helps.