There is something strange in thunar Because often what we are looking for recent files and the large size. when I want to sort a column, I click once on the date column. This is supposed to be sorted from newest to oldest. Even with "Size" column This is supposed to sort largest to smallest. But it is the opposite.
I won't take a position on what is "correct" but there's established precedent for how thunar does it. Go to http://ftp.gnome.org/pub/gnome/sources/ in a web browser and then click on "Last modified" - you'll see that the first sort is with the oldest files at the top.
Now I use qtfm that handle correctly and humanely the file sorting. Fixed!
If anything, it's a WONTFIX or needs to stay open. Since you closed it, I'll set it to WONTFIX unless a dev decides otherwise.
I'm so sorry to have flayed the status of something that rests on the foundations doing the opposite of what is described ("Last modified")