Problem with messages (text/sms)

I bought my first iPhone about a month ago (iPhone 5) and have recently noticed that some of my text messages haven't been delivered.

I'm used from my Android time to create a new message and then click on the + and select the contact I shall send the message to and choose their mobile number. But when I do this (at least recently) the receiver never receives the message, even though it looks like it's sent from the message app. I'm also pretty sure it's the correct number that will be chosen, because if i click on a contact with only their mobile number (and some e-mail addresses) I won't get the contact card up and have to choose number, which is the case with contacts with more than one phone number entered.

If I instead of clicking on the + icon just type the name and click on the correct contact and number from the search results all is fine.

I also noticed that if i select an "iPhone contact" through + and choose from contact information, the name stay green (no iMessage). If I instead don't use the + but type to search their number, it's a blue icon next to this number and the contact shows as blue and an iMessage will be sent.

It also works fine if I open the contacts app, click on send message and choose same phone number that i did during the "+ method".

Is it possible that I somehow have activated a setting that messes things up, because I'm sure you should be able to send a text message to a contact through the "+ and choose correct number in contact info" method.

 

700 views but no reply. Can't anyone of you just let me know if it's normal that you can't send text messages with the messages app by clicking on the + an choose a contact and their phone number when it works fine if you from the new message screen just type to search the contact instead?

As an iPhone newbie it would be helpful to know if I have some bad settings, sofware bug or if it's just an iPhone feature.