Hi Markus,
Thanks for contacting Syncfusion support.
We have checked the text background highlight issue you have reported and we are unable to reproduce the issue. The text background is highlighted using the background highlight tool in the RTE of the forum creation page. Please refer the screenshot below.
And we will make necessary steps from our side to retain the content in the RTE when any failure happens during submit.
Please let us know, if you have any further queries.
Regards,
Vijayakumar Y.