When working with .jar archives, their contents can be seen and extracted without any problems, despite not being (explicitly) supported, but when trying to add new files from Thunar by dragging and dropping to the Xarchiver window, a "Sorry, this archive format is not supported; the proper archiver is not installed" error pops up.
However, when using Actions -> Add, or the Add Files button, files get added without a problem.
OS: Arch Linux 64-bit, kernel 22.214.171.124-3
AMD Athlon 7750 dual-core processor
4 GiB RAM
1 GiB nVidia GeForce 9400 GT
ASUS M2N68-AM SE2 motherboard
SATA Western Digital WD15EARS 1.5 TB HDD