When adding a category to the page with the Category Selector the page is not added to the category. As soon as the 'Add' button is clicked the browser error console shows the warning
Use of "wgTitle" is deprecated. Use mw.config instead
(see 1st screenshot). Initially it appears the category has been added ('Zandbak' in my example on the screenshot) by the Category Selector, but after saving the page, the page in not in the category and a subsequent edit won't show the category in the Category Selector.
(Existing categories do show up in the Category Selector)
Interestingly enough the category name does show up in the Categories section on the page, BUT the corresponding Category page doesn't show the page, which leaves the reader totally puzzled. (see 2nd screenshot: page 'Zandbak test' shows category 'Zandbak')
The behaviour is consisted with the branches REL1_27, REL1_28 and master of MsCatSelect. I tested all 3 versions against MW 1.27
In our MW 1.26 instance using the REL1_26 branch (version ae221c5) of MsCatSelect it does show the same deprecation warning, however it works as expected.