This function is deprecated. It is provided temporarily to support porting to unique_ptr-based Cell ownership. It should be removed after the porting is done.
I have deactivated this assert for the release as it scares the users in a case we don't seem to have a problem. But we perhaps should try to find out why it is triggered.
Is there any way to handle the (perhaps, thanks to the flush commands in maxima) theoretical case that maxima might stop sending data in the middle of an XML tag and then resume sending data with the next XML packet?