How do I stop Numbers treating commas as tabs when I paste in text?

For years I have been able to use TextEdit to place column-separating tabs in text that I then want to paste into two or more columns in a Numbers file. Now, when I try to do that, Numbers makes up its own mind how many columns my text should be spread over - probably by reading commas as further tabs.

Please can some one tell me how I can stop it doing that?