When using the bulk renamer on many files (say... 1000+) each operation that causes the preview to be updated consumes memory. This memory isn't released between operations nor if the bulk renamer is closed.

After playing a bit with the Search & Replace option on 1000 files on my system, the Thunar process uses a gigabyte of memory or more and hits swap, becoming horribly slow.

The only way to reclaim the memory is to restart Thunar with "thunar -q".