1. using the -d switch from the commandline:
xarchiver -d test.tar.gz file.txt
does open the new dialog, i can change settings but the button "create" just does nothing but exits xarchiver. no matter which archive type.

2. using the thunar plugin:
rightlick on file.txt, "create archive", new dialog opens with "detect by extension" as default, file.txt as pre-entered name.
when you click create, you are warned that the file already exists and asked if you want to overwrite it. this happens even when you switched to another archive type, which is supposed to add the extension automatically.

3. from within xarchiver:
open xarchiver, open the "new" dialog, enter test.tar.gz or any other name as the archive name and then add a file by using the "add" dialog. xarchiver's statusbar will stay "Adding files to the archive, please wait..." and the stop button is enabled. nothing happens apart from that.
when you click "stop", xarchiver will ask you if you want to cancel since this will probably corrupt the archive. chosing "no" doesn't get you anywhere, so you chose "yes" which will exit xarchiver saying "Aborted" in the terminal.