This happens to me about once every couple of months.
Today I checked my blog, and realized that commenting had been turned off for all posts I have made. For no apparent reason.
So using the bulk edit feature I turned commenting back on.
I then checked the settings and noticed that commenting had been reserved for registered users, again I turned this off since I don't use user registration.
At the moment I suspect this is a security issue. Anyone else experience this?
My password is secure and I change it every couple weeks.