So I select a couple of cells in a column containing text, copy them, then double click on another cell to paste as combined text... but upon clicking into the receptive cell, the "dancing ants" disappear from my selection and the paste option is greyed out.

Fresh installation of Office 2016. No addons. No VBA or fancy stuff. Just a 3MB workbook containing text and sheets and formulas.

How can I stop wasting hours upon hours in this conniption-inducing, paste-less hell without reverting back to LibreOffice (which works just fine btw, so the more I think about it, this is probably what I should do)?