Picture changes to text

I just started to use the software and I have noticed a strange thing happening.

If I open a presentation and simply save it with another filename (I have not manipulated the file in any way) one of the pictures on the first slide will change to a TextFrame and will contain the text of one of the other TextFrames already on the slide. Can you tell me what is going on and how to stop this?

Dear Dave,

Please provide us your source presentation and source code to look into this issue.