Hi James Harrison,
Reviewing through your description above, the preview is only an approximation of the original content so some differences might occur. However, there are a couple of options you might try to generate a different preview:
1. Re-save the Powerpoint file using a different extension, for example .pptx or .ppt
2. Depending on the version of Jive you are running you might have the option to enable the HTML5 preview (admin console >> system >> settings >> new features)
Additionally, if you would like to investigate this behavior further, please submit a case in your customer group ( MyJive Secret Support Group Administration FAQ ) and provide a copy of the original file so that a member of our support team can perform testing with the specific file you are seeing the behavior with.
Thanks Jesse. It's unlikely that I'll be able to get our IT group to find the correct person to submit the original PowerPoint file, but I will try.