Are you using Hangouts or another custom MMS/SMS app? If using custom, try looking for any settings that would say to include subject line with text. If running Hangouts, I checked and there is no setting to include a subject in Group MMS or anything related to it, so the issue resides as mentioned with the iPhone user.
From the depths, the light is all you see.... Life's Good in QHD.
- Stock - No Root (yet...)
- Stock Deodexed - Root
Google Nexus 5
- Liquid Smooth - Root
Don't Forget to Hit the THANKS if I Helped!