Are you rooted? Are you using Xposed? There is a module "Disable SMS to MMS Conversion" that you could try. It references Samsung ROMs in the description, but doesn't say it's for Samsung only. Sorry, I haven't tried it myself (as I never had this problem), so can't say anything from my own experience...
Optimus G F180S, VDT V23 (KK 4.4.2)
Galaxy S5, rooted stock 4.4.2
Venue 8, rooted stock 4.4.2
To whom it may concern: STOP nagging about pressing the freakin' Thanks button!!! It is rude, stupid, and annoying as hell. I am not an idiot who needs a huge in-my-face reminder to press it, and I will press it when I feel thankful, not because you asked for it!