Well I have definitely seen people drag issues from one thread to another.
I seem to remember one girl who was I think a traveller gypsy (please correct me if I am wrong) be bashed on thread after thread. I think she offended people on one thread by having a different opinion so started another thread to explain or ask why she was being given so much grief and was put down for starting a thread about a thread to the extent that she left MN altogether.
I have seen people comment on a poster on different threads by reminding everyone of their contributions on other threads that had offended people then.
I have seen new posters being called trolls over and over again (including myself) or being told it is some sort of bad etiquette to start a thread if you are new.
And I have seen "pile on's" where a poster is ganged up on when initially having a one on one conversation and the other posters purposefully back each other up in order to shout down one individual.
I also remember a new member posting about an issue she had only to have the majority of responses be about the fact that she had used 'txt speak'. She obviously didn't have a brilliant level of English and said she was stunned as she had thought MN was supposed to be a supportive place for mum's and said she wouldn't bother coming back. I felt very sad for her as she had tried to continue the thread but felt bullied into leaving because of the way she typed, even though she wasn't from this country to have a brilliant level of English.
So yes, sometimes it does drag from one incident to another which makes it bullying in my opinion. And I personally don't think it has to be a dragged out thing to become bullying when a lot of people are involved in putting down one person or using foul language to address and belittle someone.
I get that not everyone wants to be all "oh honey" and would rather be direct and to the point, but there is being direct and to the point and there is being unnecessarily aggressive in the way someone is spoken to.
But as I said, I have also received a lot of support on here so it's swings and roundabouts. And I have a very good memory, I haven't been keeping this all written down I promise 
That's my two cents.