Added known issue per Aaron Richards for rich text control

Author: Mattp123

powerapps-docs/maker/model-driven-apps/media/html-markup-issue.png

@@ -150,6 +150,11 @@ The following sample sets the several options in the rich text editor such as th
 }
 ```
 
+## Known issue
+
+HTML markup is displayed in the field is displayed in a field configured to use the rich text editor when the field is part of a subgrid.
+![HTML markup displayed in a field on a subgrid.](media/html-markup-issue.png)
+
 ### See also
 
 [Create and edit fields for Common Data Service using Power Apps portal](../common-data-service/create-edit-field-portal.md)