I tried SFTP Net Drive as suggested. The reported versions are sftp 22.214.171.124, driver 126.96.36.1996.
Plugging USB flash drives is fine, no reboot.
I forgot to mention, that die reboot only occours, when a crypted folder is mounted.
And I encounterd a reboot on yesterday, when editing a Ms-Word document on a boxcrypter drive.