Do Not Disturb feature for Group Messaging keeps deactivating.

iPhone 6, 64GB w/ Verizon Wireless running current iOS 8.3.

I have 3 group text messaging conversations going and have activated the "Do Not Disturb" feature for each of them. However, on one specific 5 person thread (with all iPhone users), the feature keeps deactivating on it's own rendering it useless for me.

Here are some of the steps I've used to try and remedy this issue to no avail...

• Deleted the conversation and have it reappear when someone from the thread posted a new message.
• Left the conversation and had someone include me back in.
• Left the conversation and restarted the thread from my phone.
• Remove all participants from my favorites to see if it wasn't somehow connected to the feature allowing favorites to come through Do Not Disturb.

Here are some of the things I took notice that could be contributing to the issue...

• One of the contacts is still using old iOS software; however, she has always had it and the thread was working fine for a longtime.
• This seems to have happened after the update to iOS 8.1.
• One other participant in the thread is having the same problem as I, presumably after the update to 8.1... iPhone 6, 64GB on VZW up to date with iOS 8.3 as well.

Has anyone else had or is having this issue? It's really disappointing for this feature is no longer doing the very exact thing it was designed to do.