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From what I see they still have tablesorter as a plugin. Example: Zebra-striped w/ TableSorter.js

In the Google Group, Mark Otto mentioned that he didn't want to have it as a dependency (it was the only 3rd party plugin) and raised a concern with it having its own themes.

That explains a lot. It also breaks if any of the columns get too narrow. Rather than dropping the effort to further narrow it, it crushes the text of the label upwards so you are left with a set of vertically extended labels where there is ample space.