By default, DataAssist uses the replace function on all fields to replace quotes with the HTML Entity on the update page.
When you apply HTMLEditor to an update page, you will need to rebind the initial value and remove the formatting.
In the HTML Editor Instance, click the Lightning bolt next to initial Value. Select the corresponding Recordset column and set formatting to none. This will remove the replace function without having to manually edit the code.
This was documented for iRite, but has not been updated for HTML Editor.
In the Archived documentation section of the HTML Editor Support page, see the "Adding iRite to your Update page" tutorial.
I will put a suggestion to the documentation team to update that document.