Hi Alan,
Thank you for contacting Syncfusion support.
In ComboDropDown, we have handled the key of the PopUpControlContainer and we have closed the PopUp when enter key has been pressed. Due to this, PopUp has been closed in your application while pressing enter key in RichTextBox. In order to ignore the keys of the PopUpControlContainer, we request you to use the “IgnoreDialogKey” property of PopUpContainer present in the ComboDropDown control. We have prepared a simple sample in which we keep opened the PopUp when enter key is pressed in RichTextBox and it can be downloaded from the below location.
Regards,
Keerthana J