San Serif open type font switched font style on certain letters when I used Large Cap/Small Cap tool

I have a document I created using Open Sans font. No problems until I was making my last round of corrections. I typed my content into the textbook in all lower case, then clicked on the Large Cap/Small Cap tool. The "I"s showed up as seriffed letters and did not reduce to the small cap size. Also, I noticed when I typed into a new text box in all caps, the I's were continuing to appear with Serifs on them. That was the only letter that did. I reloaded by font into font book, where the preview of the font shows up correctly. It was just not appearing in my document correctly. How does such a thing happen? Open Sans is a free downloadable font. 

I appreaciate any insights anyone has to offer on this. I've never had that happen before in a font.

Deb Saxton