It happens only with Curved Text object. If you type "fi" the "i" takes space and goes under the next type. Very strange. And happens only with some fonts including Roboto.
Super weird, thanks for providing a way to reproduce this, will test
It's because there's fl / fi characters in the font. When it's a normal "text" box it changes it successfully but when it's morphing text it's not actually changing the character, just moving it to where the next character is if that makes sense.
Example here. http://i.imgur.com/wZxpFAQ.png "Text" box with correct "fi" character on top, "Morphing Text" below it.