KEYNOTE: Yellow highlighted text in KEYNOTE is NOT highlighted when exported. Why?

I highlighted in yellow a lot of the text in some Keynote slides and I can clearly see the yellow highlighted text while working on the slides but the yellow highlighting totally disappears when I click the "Play" button and after I export as a Quicktime movie and/or images.

I did this to highlight the text in yellow: Select text I want highlighted > Menu > Insert > Highlight

Can someone please tell me why the yellow highlighting around text disappears?

Thank you.

- 2008 Macbook Pro, OSX 10.9.5

- Keynote 6.2.2