The prefix printers included in pterm are initialized to use pterm.defaultWriter as their writer.

When calling pterm.SetDefaultOutput(writer) the prefix printers will still use the original default, so we need to call p.WithWriter(writer) to use a different writer.

Reading the comment of the pterm.SetDefaultOutput function I would assume the prefix printers would also use the updated default.

I have a fix for this in a local branch along with a test case, and can send a pull request if you are interested.