Yes, I do remember some folks stating that they had "white" rings in their glass but I haven't heard any such reports in quite a while. I believe, but can't attest to it, that these folks may have let it sit and soak for a long time.
That's my 'take' as well. Several of those who reported the damage 'at the time' said as much. The discussion at that time was this was not following the directions, and a bad idea. PBW is highly alkaline (which is part of why it works so good), some types of glass are more vulnerable than others I guess. Best plan is to avoid long soaks anyway, by reports they do little good. Unlike soaks in solvents, which is probably where the idea comes from.
Detergents don't dissolve the junk, they work by 'getting under it' so it can be rinsed away like food on your dishes or dirt on your clothes when you wash them. Like there, heat is important to strong action.
I guess this isn't a recommended method but it works for me. I put a small amount, maybe 1/4 teaspoon in a water piece then fill it with hot water and cork the mp opening and the joint with a rubber stopper. Then I shake it to make sure as much of the PBW as possible is dissolved in the water and let it sit for a few hours. Then I drain the water and rinse it several time to be sure all the PBW is cleared out. Works great for me.
Hey, if it works, it works? That's how it's used in breweries as I understand it. Solid, or partially dissolved PBW is introduced then 'flushed through' with hot water. After a (short) soak, it's flushed out (you can't scrub out brew kettles and plumbing there either.
I do this often personally. If I have say a stem in a 'travel tube' I then put it in a bowl of hot tap water for the five minute soak to keep it hot. Right in the sink.
The key is, I think, to not let is sit for long times if you're going to be upset with etched rings and stuff after?
BTW dishwasher detergent has many of the same features. Putting stems in the silverware rack with the dishes works great in many cases. I even rig a small funnel to some with a bit of tubing to catch more wash water and flush it through.
The stuff is really much superior to the solvent alternative. Safer (no explosion/fire issues), more effective, better for the environment (be honest most let ISO evaporate or pour it down the drain....) and it's cheaper by a long shot. It's even fun to watch the 'oxyclean' part attack years old junk in neglected bongs...... Add 'entertaining' to the list.
But as you say, be sure you rinse it all out......not good to drink I'm sure.
OF