I haven't noticed this happening to me.
BUT I did notice a case where I suddenly found an account's post in my feed that I DEFINITELY would NEVER follow.
It was @dporn
I looked to be absolutely sure, and it does not show me as following that account on their home page.
I took this screen shot on July 28th, and shared it with 3 witnesses that I know in case they had a clue what was happening, or if it was happening to other people too, but nobody had heard of it before.

The other very odd thing is that you can see the post shows as 8 hours old, between a 1-minute-old and 13-minute-old post. The only time that normally happens if it is was resteemed by someone that I follow -- yet this clearly does not show as being a resteem.

So --- is Steemit not only making us unfollow accounts but also sometimes making us follow accounts that we never chose too?
In this case, I finally decided to 'mute' the account so that I don't have to see it in my feed again.