This is one of the Wiki Renderer features. If you go to Field Configuration and change the renderer of the field, it won't act like that. However, you can't use the other features (bullets, images, attachments, ..)
And I am not aware of a solution to exclude particular features from the renderer.
Or you may search for an app about the renderers on the Atlassian Marketplace.
For more information about the Jira renderers please see this.
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