Thanks for posting this, Jelle! Can you send a pull request? If you need to learn how, check out this tutorial:
http://docs.joomla.org/Git_for_Coders

I also created a tracker item for this issue:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30857

You can receive notifications from it by signing in, going to the item, and clicking "Monitor Item" in the left column.

While we’re transitioning to a new integrated tracker, the JoomlaCode tracker is where we do most of Joomla's bug fixing. You can find out more about the process at:
http://docs.joomla.org/Filing_bugs_and_issues

I'm going to close this item, since we have the above JoomlaCode Tracker Item. If and when you submit a pull request, please reference the JoomlaCode Tracker Item URL:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30857

Let me know if you have any questions and I'll be glad to answer. Thanks again, Jelle!

Hi Nick,
the patch never merged into the core, they forgot to do it:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=29646

Hi Jelle,

Looks like they did for Joomla 3. Check out:
https://github.com/joomla/joomla-cms/blob/master/libraries/joomla/updater/adapters/collection.php#L100

It used to be:
eval('$this->' . $tag . '->_data = "";');

However, they didn't for 2.5:
https://github.com/joomla/joomla-cms/blob/2.5.x/libraries/joomla/updater/adapters/collection.php#L101

I'll go ahead and report it for 2.5 on JoomlaCode. Please follow that discussion there. Thanks! I'm going to close this one.