Error formatting DVD-RW with usb recorder

When I try to format a previously written DVD-RW with my USB recorder, I obtain the error reported below which I suppose is related with the fact that the DVD is automatically mounted with pmount (I'm using Kubuntu Edgy Eft upgraded from Dapper) when I insert it.
In order to format the dvd, I have to use the console to manually umount the /media/dvdrecorder and after that K3b works correctly.
If I insert a blank DVD, it isn't mounted automatically and so K3b works flawlessly.
If I start K3b as root there is no problem, but it's not very safe.
What can I do to format my DVDs using K3b as user?
Thank you,
Xwang

System
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K3b Version: 0.12.17

KDE Version: 3.5.5
QT Version: 3.3.6
Kernel: 2.6.17-10-generic
Devices
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HL-DT-ST DVDRAM GSA-4082B A201 (/dev/scd0, /dev/sg0) at [CD-R; CD-RW; CD-ROM; DVD-ROM; DVD-RAM; DVD-R; DVD-RW; DVD+R; DVD+RW] [DVD-ROM; DVD-R sequenziale; DVD-RAM; DVD-RW a riscrittura limitata; DVD-RW sequenziale; DVD+RW; DVD+R; CD-ROM; CD-R; CD-RW] [SAO; TAO; RAW; SAO/R96P; SAO/R96R; RAW/R16; RAW/R96P; RAW/R96R; Riscrittura limitata]

MATSHITA UJDA750 DVD/CDRW 1.51 (/dev/hdc, ) at /media/cdrom0 [CD-R; CD-RW; CD-ROM; DVD-ROM] [DVD-ROM; CD-ROM; CD-R; CD-RW] [SAO; TAO; RAW; SAO/R96P; SAO/R96R; RAW/R96R]
dvd+rw-format
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* DVD±RW/-RAM format utility by <email address hidden>, version 6.1.
* 4.7GB DVD-RW media in Sequential mode detected.
umount: /media/dvdrecorder non si trova in fstab (e non si è root)
:-( unable to proceed with format: Device or resource busy

dvd+rw-format command:
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/usr/bin/X11/dvd+rw-format -gui -blank /dev/scd0