With the beta-feature currently deployed at beta cluster, I cannot use shift+click to select a group of checkboxes.
If I left-click (enable) the top checkbox at http://en.wikipedia.beta.wmflabs.org/wiki/Special:EditWatchlist
and then shift+left-click the 5th checkbox, it does not enable boxes 1-5 inclusive.
I can do this at https://en.wikipedia.org/wiki/Special:EditWatchlist
or if I turn off the beta-feature at beta cluster.