Text boxes are changing fonts on their own

I've suddenly been having an issue with text boxes in illustrator. 

When using a text box, sometimes the font randomly changes. For example if I am typing in Arial but then select the whole text box and chnage the font to Times, when I continue typing it just starts in Arial again.

I contacted adobe support about this and they told me it was because I was using character or paragraph styles. However I am not using either, and this issue still persists even if I start a brand new Illustrator file. 

It doesn't happen consistantly either though. Only some fonts, only some text boxes and only some files. Please help, I feel like I'm going crazy.