On cswiki we encounter like 30 articles per month, which are starting with <br>. It seems that this is included, when someone removes the text at the beginning of the page, see e.g. 1 or 2.
You can search our articles beginning with HTML tag maintenance list for other examples (see the last update for example)
Perhaps even more than 30 per month, but many are fixed before the maintenance list is updated.
BTW perhaps has something to do with Infoboxes/other top templates?
I think there is some unresolved confusion around whether this is a Parsoid fix or a VE fix .... I'll chat with matmarex on irc and resolve this. But, if this turns out to be something that Parsoid needs to do, given that we are currently in porting mode, we won't prioritize this unless this is a high priority fix needed by VE.