And here is my problem of understanding, why, I am of the opinion that everything is reloaded and then recalculated, so there shouldn't be a message that irritates me more than it helps?
this is just seen as a hint, that it might be an unwanted result, as there are no matches between those two tables.
Try to add one of the values of table 2 in table 1 (or the other way round), and there won't be any warning, as at least one match is there.
In case, you you know that this warning could happen and it will be okay for you, you can suppress it as follows:
And: thanks for the files. That makes it much easier!