fix custom sorter test

Fixes the occasionally randomly failing paginated table test.

Officially closes #2147 

Since sorting happened by name, if you have 2 columns with the same name, it messes up the sorting

The test failed because, randomly, the test would result in a table where the 1st and 2nd columns had the same name, and since it sorts on the 2nd column in the test, but *actually* sorts on the first match (1st column) internally, the test would fail

It's actually a bug in the paginated table, which will require a fix and a new test. Opened #2219.