Hi Brian,
Thank you for your interest in Syncfusion Products
Currently Essential DocIO provides only preservation support for Content Control.Could you please report this issue through Direct Trac Developer Support System (https://www.syncfusion.com/account/login?ReturnUrl=%2fsupport%2fdirecttrac%2fincidents because you can take the advantage of the expertise of a dedicated support engineer and a guaranteed response time and we hope you will take advantage of this system as well. If you have already reported, please ignore this.
For more information on Content Control in DocIO , kindly refer below link:
http://help.syncfusion.com/UG/Reporting/DocIO/ASP.NET/default.htm#!documents/434contentcontrol.htm
Please let us know if you have any other questions.
Regards,
Ramkumar