If noticed this several times now but it occurs randomly.

I have a Synchronization job running which syncs ticket information between Mantis another system.
In the screenshot below you see an example.

The case:
The Synchronization job updates a random field (in this case the field 'Patch' which is a custom field
in my system) and this is intentional. In the same update however an "empty" update of the description field was triggered.
I had to obfuscate the text in the screenshot but a Diff programme showed NO differences between the two versions, the text is exactly the same.
Furthermore, the source code of the Synchronization job includes not a single line that refers to any update of the description field,
that is why we can exclude that the update was caused due to a change of the (for the user invsible) HTML tags between two versions.

I have seen this happening only in updates that are triggered through the API.
It affected only the default multiline text fields so far, hence 'Description', 'Steps To Reproduce' and 'Additional Information'