Thanks for your bug report.
The /window code actually checks for an empty -t and redirects the call so that it does not create a window. I can't say why, as it was added so long ago, but it looks like it was intentional. It would be easy to fix but considering it has worked this way ever since it was created, I am not too keen on changing it.
In
versions.txt, it is listed as [-tN,..,N], so there is a discrepancy there from the help file.
It also looks like you can update the tabs of an existing @window by using /window -t N N N ... although this is not documented in the help file but is mentioned in
versions.txt (v5.61, item 55).
