How so? As a novice I'm wondering what this and other red flags say about an author, and why.
I shall answer this in three separate ways.
1) POV shifting is not only off putting to a certain segment of readers (I gain this knowledge both from personal and professional opinions and the professional part has nothing to do with me).
It is considered kind of like a lack of focus that's common to new writers. A writer has all sides of the conflict in his head and wants to fully express them. This often causes clunky, attention splitting scenes that confuse the readers unless done well. There's other things, duplication of effort (things seen twice from two different views), or the readers don't want to invest in anyone but character A and get frustrated that they're forced to follow, B, C, and/or D.
Older writers can and have gotten away with it but if you look multiple POV's are less and less common since the 80's and 90's books. You still get the occasional game of thrones massively multi-POV out there which is why workmaker and I aren't exactly poopooing the idea. But even among the professional authors its becoming more and more of rare beast.
2) What does it say about the novice?: a few years back I was tooling around on the Baen Slush Magazine section. the one that helped feed the online magazin eric flint used to help produce. I uploaded a short story about some... well it really doesn't matter what it was about. Anyway I spiffed it up as best I could at the time and uploaded it for the group that's hanging out there to take a look at. I got basically got a 'come back when your worthy response'. Your story needs work, your character development isn't quite rich enough and what was up with this flicking the marble in his hand couldn't even follow it after three reads, on top of that if you don't care enough about your story to fix your grammar etc, why should an editor. Despite my initial hot headed reaction to this response to my little masterpiece, I managed to throttle myself down to a gruff but not surly, 'well that's your opinion.' To which the person responded 'I don't know why I bother sometimes'. A day or so later I was tooling around the site and what to my wondering eyes did appear? The person that had thrown her verbal hands in the air at my current lack of skill coupled by a defensive response was none other than the top editor of Baen, Toni Weispkoff. Suddenly I was no longer upset I was instead instantly grateful I hadn't gone with my initially desires (thin skinned writer) response and kicking myself that I hadn't recognized this person and solicited their advice further and uploaded a revised version as rapidly as I possibly could.
Now I'm not saying this applies to anyone here (that was part of my learning curve as a writer that I just happen to share because it was related to a red flag incident). What I am saying that with a red flag situation you'll tend to get a 'come back when you're worthy' response from the professional editor. Your job with a red flag is to sell your story past this speed bump, to have such awesome coolness that people are saying 'he broke the mold with this one' instead of 'what another tired old trope' and one that off puts most readers to boot, so here's another for the round file system (click).
Alternately in the world of direct publishing, instead of editor rejection you get the old vote with their feet response.
When I first started writing I was told to fight the urge to POV shift with all the strength in my body. Now in part that was because my first few stories had this component and I clearly wasn't able to do my story justice when I was doing it. Maybe someone else is much better at it. I know I'm not only head and shoulders better than my younger self at different POV's, I've climbed a whole dang hill. Just because I wasn't able to do it justice early on doesn't mean you shouldn't try it out. I'm just saying its a common pitfall for new authors for a reason. Almost everyone who tries it falls into the pit, just be warned and hone your craft young padawan.
The Deposed King
P.S. - I think wordmaker may have said this better than me but it sure seemed like a waste to just toss 20 minutes worth of work.