hi Michal

>> Well as far as it goes it should do no harm but in my opinion it
>> could most certainly be dropped.
> I've found this comment in the literate sources:
>> The following is to ensure that no shipout of content is done
>> before the header is out.

> So there was probably some case where it caused problems. In my
> tests, removing this shipout didn't cause any harm, so I will do it.

well I would claim it can apply to LaTeX. Not when the header is written 
by the appropriate hook, whether that is \AtBeginDvi or its form in the 
new hook management system.

maybe there was a use case for plain but I  doubt even that. If there is 
content before the header you would need to get rid of it basically by 
getting to the OR and then throwing box255 away and this is not what the 
code does.