Thanks for the clarification.

Now that you've answered, I feel embarrassed by how easy it was to set the default data source.

But I must say, the error message is a bit confusing. If there's no way to set a default key:value pair from a termlist, why is the default editor available?

Thanks for the reply.

CASCADE means that the data is deleted also in parent and child tables, RESTRICT means that only parent data is deleted. Changing the default RESTRICT does nothing, the data is still there

Any other option?

UPD: i've managed to delete data with

UPDATE TABLE table SET column = NULL

But issue is still open, why %DELDATA do nothing

As far as I understand from your answer, I have no choice but to apply some hacks to my data. This is unfortunate. I was thinking about using a hash too. I think I will do that.