Please note that it's not a bug in Launchpad. The issue is that xgettext extracts the string and interprets it as a format string "%c":
#, c-format
msgid "% chance"
msgstr ""
Then Launchpad displays it and does error checking interpreting it as a format string, as marked in the .pot fie "#, c-format". I believe one way to work around this is to mark the original string as "%% chance" (see the double percentage mark), but I've not tried it myself.
Please note that it's not a bug in Launchpad. The issue is that xgettext extracts the string and interprets it as a format string "%c":
#, c-format
msgid "% chance"
msgstr ""
Then Launchpad displays it and does error checking interpreting it as a format string, as marked in the .pot fie "#, c-format". I believe one way to work around this is to mark the original string as "%% chance" (see the double percentage mark), but I've not tried it myself.