Hello!
I setup a similar process and there does seem to be an issue with the clearChangeset() functions not working as intended. However, I was able to save the data from a new row using a Save Event handler without any issue.
When you use the add row function, the data is stored in the newRows property array (even though current usage only allows one new row at a time). The Save Event should be the same one you would use for other existing row data changes but you'll likely need to handle both the changesetArray as well as the newRows. You could have separate queries for them and use the Save Event to pass data via additionalScope or perhaps merge them together in your update/insert query.
To get around the clearChangeset() function not working I just added a Success event handler on the triggered Save Event query to refresh the table and re-trigger the query for the data source.