When one opens a document, spellchecking is turned on/off depending on the spellchecking in last active document, independent if that is Calc, Writer, ...
It would be more convenient if opening/starting a Writer-doc looks at spellchecking in last active Writer-doc; not at the situation in e.g. an active Calc-document.
It's a valid feature request.
There are people who do not need automatic spell checking in a spreadsheet, but need it in a word processor.