Comment 5 for bug 1622131

Same argument applies. Say I set the temp dir to a path on a mounted volume that is secured in some way or has some other special properties, say via mount flags. If the mount fails, this patch will cause calibre to create the temp dir on the underlying filesystem and happily use that with the user being none the wiser. If the underlying filesystem is an NFS share, you just exposed calibre temp files to the network.

Overriding an explicit user setting should be done with some form of user feedback, as the original bug report asked for.