ubiquity crashed in run() with UnicodeDecodeError when mount point contains accented character

TEST CASE:
1. Launch ubiquity and proceed to 'Advanced Partitioning'
2. Create a partition and enter a mount point with an accent

result:
Ubiquity crashes with:
Exception caught in process_line:
Traceback (most recent call last):
  File "/usr/lib/ubiquity/ubiquity/filteredcommand.py", line 132, in process_line
    return self.dbfilter.process_line()
  File "/usr/lib/ubiquity/ubiquity/debconffilter.py", line 281, in process_line
    if not input_widgets[0].run(priority, question):
  File "/usr/lib/ubiquity/plugins/ubi-partman.py", line 2686, in run
    self.preseed(question, request['mountpoint'], seen=False)
  File "/usr/lib/ubiquity/ubiquity/filteredcommand.py", line 336, in preseed
    value = value.encode("UTF-8", "ignore")
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 4: ordinal not in range(128)

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: ubiquity 2.7.17
ProcVersionSignature: Ubuntu 3.0.0-9.14-generic 3.0.3
Uname: Linux 3.0.0-9-generic i686
Architecture: i386
CasperVersion: 1.279
Date: Thu Aug 25 14:37:24 2011
LiveMediaBuild: Ubuntu 11.10 "Oneiric Ocelot" - Alpha i386 (20110825)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)