I hate to revive this too, but I started having the same problem today as well. Nothing has changed on my computer since the last time I took notes in Word 2011 (yesterday.) Everything is always kept up-to-date and there were no new software updates installed this week.
Today when I opened up some class notes, I noticed that when tabbing through levels, I could no longer hit enter/return and then delete to move the next line up one level. It just retreats up to the previous line.
Has anyone else figured out the solution, other than switching to shift + tab?
Microsoft Word is absolutely infuriating, and about once per semester for whatever reason, the bullet settings on my program change and the bullets don't respond normally to the tab/delete buttons. It takes me about a day of swearing and throwing things to rediscover how to fix it each time.
Here's how (I use Word for Mac, so may be a bit different if you're on Windows):
(1) While in Word, on the OS toolbar select "Word."
(2) In the drop-down menu, select "Preferences"
(3) In the new pop-up window, select "AutoCorrect"
(4) In the next window, there are three separate tabs at the top. Select the middle tab titled "AutoFormat as You Type"
(5) Towards the bottom of the new screen, there is a checkbox for "tabs and backspace set left indent." This is your problem. Check it, or uncheck it depending on your preference. For whatever infuriating reason, Word likes to randomly uncheck mine at periodic, incredibly inconvenient times.
Hope that helps.