Email Hyperlink Breaks
In the Hyperlinks panel, Email hyperlinks that include a subject that includes an ampersand will change from an Email-type to a URL-type when you click OK. Status will then appear as a red dot in the Hyperlinks panel instead of an envelope. Opening it again from the Hyperlinks panel will show the subject gone and in a URL format.
TO TEST - Highlight text in your document. Open the Hyperlinks Panel. Create a new hyperlink with the [+] button at the bottom of the panel, choose email as the type, type a valid email address, then enter a subject line that include an ampersand (&) . Click OK.
THE FIX - Removing the ampersand from the subject line will keep the issue from occurring.

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Keith Cross commented
I've seen this behavior as well when trying to test if adding "&body=body message" would populate the body of the resulting email. Fun fact, it does not populate the body. It would be great to fix this bug, AND to add the ability to populate the body with a simple message.