I'm using a stock tracker with roundup 1.6 (the tip less a few of the 
latest patches). I'm using python 3.5, Ubuntu 16.04, postgress 11.1, and 
a few other things that might be of interest.

I created 3 issues with various keywords (see screen dump). Then I did a 
search grouping on keyword and got the search results page. I wanted to 
reverse the order so at the bottom of the page checked the 'Descending' 
checkbox for 'Group on' and clicked 'Redisplay'. The 2 issues at the top 
changed order but the bottom one stayed there. I expected the ordering 
should be reversed from ascending.

I attached screen dumps for the two sorting cases. The issues can be 
recreated easily. This may be related to issue 2551013.

Roundup 1.4.21 has the same behavior.