Just installed release 10.10 (rev 197) and there was no permission denied.
Repeating rev 236 test to confirm that this is a regression (rule out any
variation due to 'rebooting windows'.)

Confirmed regression: I only get this permission denied with 11.10.

10.10's log looks like this (so it is also trying to hit the Q: drive):
09-29 15:11 DEBUG  TaskList: ## Running create_preseed...
09-29 15:11 DEBUG  TaskList: ## Finished create_preseed
09-29 15:11 DEBUG  TaskList: ## Running modify_bootloader...
09-29 15:11 DEBUG  TaskList: New task modify_bcd
09-29 15:11 DEBUG  TaskList: ### Running modify_bcd...
09-29 15:11 DEBUG  WindowsBackend: modify_bcd Drive(C: hd 234451.042969 mb
free ntfs)
09-29 15:11 DEBUG  registry: Setting registry key -2147483646
Software\Microsoft\Windows\CurrentVersion\Uninstall\Wubi VistaBootDrive
{06eb1e43-eae8-11e0-b3af-543211c77614}
09-29 15:11 DEBUG  TaskList: ### Finished modify_bcd
09-29 15:11 DEBUG  TaskList: New task modify_bcd
09-29 15:11 DEBUG  TaskList: ### Running modify_bcd...
09-29 15:11 DEBUG  WindowsBackend: modify_bcd Drive(F: hd 12320.453125 mb
free ntfs)
09-29 15:11 DEBUG  WindowsBackend: BCD has already been modified
09-29 15:11 DEBUG  TaskList: ### Finished modify_bcd
09-29 15:11 DEBUG  TaskList: New task modify_bcd
09-29 15:11 DEBUG  TaskList: ### Running modify_bcd...
09-29 15:11 DEBUG  WindowsBackend: modify_bcd Drive(Q: hd 0.0 mb free )
09-29 15:11 DEBUG  WindowsBackend: BCD has already been modified
09-29 15:11 DEBUG  TaskList: ### Finished modify_bcd
09-29 15:11 DEBUG  TaskList: ## Finished modify_bootloader


And 11.10 like this:
09-29 15:38 DEBUG  TaskList: ## Finished create_swap_diskimage
09-29 15:38 DEBUG  TaskList: ## Running modify_bootloader...
09-29 15:38 DEBUG  TaskList: New task modify_bcd
09-29 15:38 DEBUG  TaskList: ### Running modify_bcd...
09-29 15:38 DEBUG  WindowsBackend: modify_bcd Drive(C: hd 234444.207031 mb
free ntfs)
09-29 15:38 DEBUG  registry: Setting registry key -2147483646
Software\Microsoft\Windows\CurrentVersion\Uninstall\Wubi VistaBootDrive
{06eb1e44-eae8-11e0-b3af-543211c77614}
09-29 15:38 DEBUG  TaskList: ### Finished modify_bcd
09-29 15:38 DEBUG  TaskList: New task modify_bcd
09-29 15:38 DEBUG  TaskList: ### Running modify_bcd...
09-29 15:38 DEBUG  WindowsBackend: modify_bcd Drive(F: hd 12320.453125 mb
free ntfs)
09-29 15:38 DEBUG  WindowsBackend: BCD has already been modified
09-29 15:38 DEBUG  TaskList: ### Finished modify_bcd
09-29 15:38 DEBUG  TaskList: New task modify_bcd
09-29 15:38 DEBUG  TaskList: ### Running modify_bcd...
09-29 15:38 DEBUG  WindowsBackend: modify_bcd Drive(Q: hd 0.0 mb free )
09-29 15:38 DEBUG  WindowsBackend: BCD has already been modified
09-29 15:38 DEBUG  TaskList: ### Finished modify_bcd
09-29 15:38 DEBUG  TaskList: ## Finished modify_bootloader
09-29 15:38 DEBUG  TaskList: ## Running diskimage_bootloader...
09-29 15:38 DEBUG  WindowsBackend: Copying
C:\Users\bcbc\AppData\Local\Temp\pylCF8F.tmp\winboot -> C:\ubuntu\winboot
09-29 15:38 ERROR  TaskList: [Errno 13] Permission denied: 'Q:\\wubildr'
Traceback (most recent call last):
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\win32\backend.py", line 482, in
diskimage_bootloader
  File "\lib\shutil.py", line 39, in copyfile
IOError: [Errno 13] Permission denied: 'Q:\\wubildr'
09-29 15:38 DEBUG  TaskList: # Cancelling tasklist
09-29 15:38 DEBUG  TaskList: # Finished tasklist
09-29 15:38 ERROR  root: [Errno 13] Permission denied: 'Q:\\wubildr'
Traceback (most recent call last):
  File "\lib\wubi\application.py", line 57, in run
  File "\lib\wubi\application.py", line 131, in select_task
  File "\lib\wubi\application.py", line 157, in run_installer
  File "\lib\wubi\backends\common\tasklist.py", line 197, in __call__
  File "\lib\wubi\backends\win32\backend.py", line 482, in
diskimage_bootloader
  File "\lib\shutil.py", line 39, in copyfile
IOError: [Errno 13] Permission denied: 'Q:\\wubildr'