Editing the wikitext appears to function correctly, which is good news.
https://it.wikipedia.org/w/index.php?title=Matematica&diff=60342095&oldid=59678552

{{BeginKolommen}} generates the beginning of a table, and {{EindeKolommen}} generates the end of that table. All content between those two is treated as one template call. This is expected behavior in the current implementation, and is exactly the same as succession boxes and all other templates that generate openings and closings separately (multipart templates).

It would be nice if we could let users edit these in a nicer way, especially considering that some (but not all) of the wikitext blocks are actually innocuous wikitext that VE could reasonably edit, but right now we can't. This is part of the reason why multipart templates suck.

What is the Parsoid topfail thing you're talking about? There's no link to the failure and it seems unrelated to this issue.

Not closing this as INVALID or whatever because this is something we should actually handle better.

I think it is impressive that VE handles it

'nl:Eerste divisie 1996/97' is on the parsoid topfails list

http://parsoid.wmflabs.org:8001/topfails

Here is an itwp example where multicol consumes most of the page, and should probably be removed.

https://it.wikipedia.org/wiki/Campagna_%28comune%29?veaction=edit

(In reply to comment #3)

I think it is impressive that VE handles it

This is mostly thanks to Parsoid handling this case very well, and VE simply building a UI around it :)

'nl:Eerste divisie 1996/97' is on the parsoid topfails list

http://parsoid.wmflabs.org:8001/topfails

Oh, I see. It's not any more now :(

Here is an itwp example where multicol consumes most of the page, and should
probably be removed.

https://it.wikipedia.org/wiki/Campagna_%28comune%29?veaction=edit

Yes. I just fixed that page.

(In reply to comment #4)

'nl:Eerste divisie 1996/97' is on the parsoid topfails list

http://parsoid.wmflabs.org:8001/topfails

Oh, I see. It's not any more now :(

It is on page two of 16

http://parsoid.wmflabs.org:8001/topfails/2

I have no idea if the {{BeginKolommen}} or tables within it have anything to do with the semantic failure; just thought I should mention it.

(In reply to comment #5)

(In reply to comment #4)

'nl:Eerste divisie 1996/97' is on the parsoid topfails list

http://parsoid.wmflabs.org:8001/topfails

Oh, I see. It's not any more now :(

It is on page two of 16

http://parsoid.wmflabs.org:8001/topfails/2

Aha! Found it.

I have no idea if the {{BeginKolommen}} or tables within it have anything to
do
with the semantic failure; just thought I should mention it.

That doesn't appear to be the case: looking at the RT diff (which you get to by clicking on the page name), it's mostly related to the tables on the page: http://parsoid.wmflabs.org/_rt/nl/Eerste_divisie_1996/97