Tabular Parser - appending again parsed line when saving

I tested the feature that today @josma asked in the Fairmat café when @amgo showed the new features.

First, I parse an excel sheet into a section instances with "row" mode. If then I want to add manually a new instance, I can do it via the "plus" button; when saving I get my section instance correctly placed but I also get another set of parsed section appended below (see image).

I'm thinking that this issue is tightly connected to #823.

I recall that when I save I am also adding the processed data into the json archive. While these things are only stored in memory when uploading the schema and excel file and getting a "success" outcome from first processing.

One can think to have the save button split in two, one is processing and one is only saving, or something like that