I have that by add a sum in a column gives a date

To be more clear you can see it in column two, and column six.

Sorry in my English or even my Dutch I always make mistakes, but bugs like this I can eat my socks for it.

Row two? Row six??? On a screenshot where rows shown are in range 468-492, and when counting from top, the date is 22th row?

Could you please provide a sample document here? Put it to some online share, and post a link in an edit to the question. Thanks!

I first have made a csv data from it, imported it as a normal column and than copied it to an old tab, this worked well, although I cannot understand what happened. To import it as normal you have to right click on the column. I do not understand how to answer in this thread actually; oh only one answer per user is allowed)

As I mentioned: your previous “answer” should have been comment; and this your comment should be answer (though pity you didn’t provided the file to check, so that others could try to understand and eithet describe what’s wrong, or, if it’s a bug, file it to bug tracker).

You may edit your answer.

Yes my comment is the answer, you first have to save a column as csv, than open it and copy it to the tab, than cut it in pieces, if you like and than make the sum. https://drive.google.com/open?id=1q3gx5nlvPtAuQInFiygK8pja07mShKQv

The format seems to be the normal format, when I press ctrl + 1 nothing seems to be wrong. Maybe I should format the column first as text and then copy it to the first tab. This is the old comment.

Hey! You have shown the problem at your initial question’s screenshot. Is it that hard to provide the ODS file which shows the problem?! How am I supposed to see the problem from your CSV???

Well, I guess that even I don´t know the problem, you can see it at the screen shot, but I think that saving it to a csv file made it clean so that you can copy it to the other tab.

Just format (Ctrl+1) cells as numbers. You seem to have copied the formatting from somewhere where the dates were used; or initially put dated there, and the formatting was detected and set. In LibreOffice, dates are just numbers that represent time elapsed from epoch, with special cell formatting.

Somebody who think this is the answer is wrong, because copying it from another spreadsheet has a bug, and you don’t take this seriously. And it worked perfect saving it as a csv file.

Yes my comment is the answer, you first have to save a column as csv, than open it and copy it to the tab, than cut it in pieces, if you like and than make the sum. https://drive.google.com/file/d/1q3gx5nlvPtAuQInFiygK8pja07mShKQv/view?usp=sharing