speech balloons changing color in Presenter

I'm working with a presentation someone created in PPT 2010, and which includes speech balloons selected from the PPT shapes menu. Text is typed directly into the balloons. (Not text-boxes on top of a balloon.) When I preview or publish in Presenter, some of these white balloons with black text look fine and others appear as dark gray balloons, (Text is still visible.) In some cases the balloon is dark gray and also appears upside down and on another part of the slide.

If I delete the balloon and insert a new one of the same type, it is fine when previewed or published.

The creator is using PPT 2010 and a pc.

Do you have any idea what may be causing this and how we can fix it, short of my having to delete and re-insert each non-functioning balloon before I publish it?

Thank you.

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