Comment 3 for bug 451811

The problem is this line:
os.system( "crontab -l | grep -Pv '(?s)%s.*?backintime' | crontab -" % system_entry_message )

Running just
$ crontab -l | grep -Pv '(?s)#Back In Time system entry, this will be edited by the gui:.*?backintime'
on the command line returns:
grep: Support for the -P option is not compiled into this --disable-perl-regexp binary
on stderr and nothing on stdout, which feeds into crontab - and wipes out everything in the crontab.

Upgrading grep to version 2.5.4-4 from the testing repository adds support for the -P option, but a lot of people will probably be using debian stable for a while still.