My charger cover also broke off after about a month. Called Samsung and they want me to send my phone in to assess if I damaged it or it was a defect. I was VERY careful with the cover. I think this is becoming a common issue which is an indication on a problem. I am also expected to send to Samsung at my expense.
I think it is a problem with the adhesive used to attach the cover. I have to send them my phone and wait about 2 weeks or so to get it back. I'm not pleased with this, but without the cover the phone isn't waterproof...which is one of the reasons I bought it. This phone wasn't cheap. I've been team Galaxy since Galaxy S. I'm looking at HTC for my next phone.
Please understand that even with the cover the device isn't waterproof. Its IP67 Certified which means its water resistant and that by no means you should go swimming with it or intentionally submerging it into water.
With that out of the way its important to remember that the cover snapping from the phone doesn't impact the water resistance. The only thing this does is force you to keep track of the cover which in itself is unacceptable. With that said I understand the annoyance and its a bad design by Samsung. We just need misinformation at a minimum here so I'm clarifying.
As for sending the device in to Samsung I'd avoid doing so. Samsung will just replace the cover with the same cover you had break once and you'll be down this road again. My cover is holding up just fine but I only open it up just wide enough for the charging plug to have room to plug in. I'm not sure how much others are doing it but that's my experience and so far so good.
Lastly, don't jump on Team HTC just yet. Read the HTC One M8 forums here and check out the camera lens issues. Scratched lenses all over that impact image quality.
Samsung Galaxy S5 (Verizon)