Well, there was definitely a bug in the thumbnailer that relates to relative pathnames, and I just picked up on the error message you copied.
If there is a virtual filesystem somewhere, the thumbnailer has no idea that it exists. In a nutshell, the thumbnailer can produce a thumbnailer for a path in the filesystem, no more, no less. If there is no path, there is no thumbnail :-(
Well, there was definitely a bug in the thumbnailer that relates to relative pathnames, and I just picked up on the error message you copied.
If there is a virtual filesystem somewhere, the thumbnailer has no idea that it exists. In a nutshell, the thumbnailer can produce a thumbnailer for a path in the filesystem, no more, no less. If there is no path, there is no thumbnail :-(