Please see screenshot attached. I have noticed the inconsistent with TinyMCE’s plugin. I wanted to clarify that with you first.
In Photoshop, click File > File Info… and that’s the place where you can add image description, keywords, etc. then we export “Save as for web” (in “Save as for web” setting… as long as you select metadata to “all” to show image description…)
On Mac, we do Command + i (Get Info) on the image (see top left) and it showed Image Description and Keyword. That’s good.
Anyway, when we uploaded to Wordpress, it automatically added in Caption box (see top right) and that’s still good, too!
When we upload to Percussion, it doesn’t automatically add Image Description (bottom left) nor in RTE (Rich Text Editor which is on bottom right).
Can you double check to ensure TinyMCE plugin transfer the Image Description automatically in Percussion? This is important in term of Accessibility issue.