Unlocked Verizon S5, trying to use it on a German carrier, having some problems with messaging...

[MEDEL514]

So far, everything seems to work great on this unlocked US Verizon phone on the German carrier T-mobile.de, but I'm having some problems with messaging. When I get a text from someone and go to immediately reply to it, I get the "failed" to send message. The only way I can rend a reply is to go into my contacts folder, go to the contact, hit the envelope (message) icon which takes me back to the message, then I am able to reply to the original message.

It's pretty strange that I have to go through my contacts to reply, but I can't reply directly to the incoming text. Does anyone have any idea whats going on?

 

[MEDEL514]

Here's a quick screen shot of what I'm dealing with, it shows the reply that didn't go through, and the two that did because I had to go through the contact first.