Fixed in 1.1a1

Issues addressed by following patches are already fixed in IronPython 1.1a1. You are advised to upgrade.

patch-ironpython-file-canseek
This patch lets IronPython to avoid accessing Position attribute of underlying stream when it is not seekable.
patch-ironpython-open-unknown-mode
This patch lets IronPython to ignore unknown mode characters in open builtin function.
patch-ironpython-re-lastgroup
This patch implements lastgroup attribute of match objects produced by regular expression matching.