I meant by inserting the flanged Ety's you push air out...letting go will immediately create vacuum type pressure. Obviously not as much as an issue with foamies.
I can't say I've had similar problems, but if you do become an expert at insertion and seals I don't think it would be an issue. However the fact that the ER6 is short and squatty with only 2 flanges probably makes it more of an issue than ER4. Than again it can all depend on the speed at which you yank anything out of your ear. Again yanking isn't an issue for me perhaps with ER4 shirt clip or equal length cord. Wearing cording on the back might help.
I still wouldn't discount the value of proper insertion which is not as trivial as one would think. Overcompensation and cramming something deep into your ears just so that it stays there is not uncommon. When you can insert them in less than 5 seconds, at a depth that is neither too deep or shallow, in a manner that doesn't create pressure imbalance, I don't know if this issue is that much a problem especially with ER4's. For me the risk of this problem is about as high as accidently listening with the volume maxed out. Yah its a dangerous possibility...but it should be known by now...Ety's require the responsibilities of expertise, care, and sense above and beyond other headphones.
Anyhow after using ER4's with rubber flanges for a long while...this isn't an issue for me...if there was the occasional tug on the cord it would distribute force on both sides of the phone...and being that it would have to be a downward pull, it would do very little but either mess up my seal, or just pop out harmlessly. So yah...if I deliberately shoved my ER4's a bit too deep...than forcefully pulled em out...yah that could easily be harmful. But I don't see many circumstances for which I could reproduce it in normal use as a veteran user...just like I probably wouldn't be caught listening with the volume accidently maxed.
A few ER4 users seemed to say the ER6 seemed more difficult to insert. I know that the ER4 are longer and more slender while the ER6 are shorter and fatter. With the amount of posts that seem to say, "I thought I figured it out...but THIS time I think I finally figured it out", when it comes to Ety insertions, I can only say that you may think you got a seal the first times around...but there still is a high possibility that it isn't THE "Ideal" seal.