probably you have cc 2015.
you should upgrade your indesign.
however go to
Preferences > Display Performance and set the 'Greek Type Below' to 0 pt.
Yes. I can recall—I hope that I'm right—that this problem was a bug in one of the lower versions of InDesign CC 2015.
Shouldn't be the case with InDesign CC 2015.4.1, I think.