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Colon in a URL results in blank page

New YACS user here with a bit of a showstopper...

I'm just starting to evaluate YACS 7.1 as an intranet replacement but I've encountered a bit of a problem. If I go to any URL that contains a colon in the string (e.g. /yacs/versions/list.php?anchor=article:9) then two things happen:

1. The colon gets URL encoded (/yacs/versions/list.php?anchor=article%3A9)

2. A blank page results

Is this something peculiar to our installation or is this a recognised bug in YACS?

We're using a LAMP setup (CentOS, Apache 2.0.52, PHP 5.1.4, MySQL 4.1.20) and I've ran the upgrade scripts to make sure we're up-to-date.