To reproduce create the following page with some image.

The Wiki markup is:

Some text before

Some text after

In Confluence 2.9 you could switch between Wiki markup and Rich text without breaking something.
Since 2.10.1 however there is a regression!

First time you switch to Rich text everything appears fine, but if you go back to Wiki markup it is:

Some text before
!image.jpg!Some text after

Switching back to Rich text and the image disappeared and the rich text itself is:

Some text before
!image.jpg!Some text after

Next time you switch to Wiki markup it is escaped to:

Some text before
!image.jpg!Some text after

etc.

Current workaround for Confluence 2.10.1 is to add a line break after the image, e.g.

Some text before

Some text after

works without round-trip problems in Confluence 2.10.1. In 2.9. this wasn't necessary.