demo not the same as download

after update Author make demo for script,
but the download files is not the same as in demo.
is legal ???

Depends on the item, what the differences are, if there is demo content to be installed etc

Some function is not present in the downloaded file, but we can see it in demo (base function).
This is not a clean way to get Support payment.

Its hard without seeing/using the file - your best option is to contact the author How to contact an author – Envato Market Help Center