Ah, you are correct about the security. The whole point of the text format filter is to block all the possible malicious tags. I tried playing around with the filter settings, but it didn't make a difference.

As I can't find several other people reporting a same kind of issue, it sounds more like my drupal installation is somehow corrupt. I quickly checked my filter module, and it seems to be intact. But, maybe it isn't the filter module in itself, but some other part of the drupal core. I have to do more testing in the evening. Ah, and I posted a question on Drupal forums, hoping that someone would point me to the obvious solution which has been right front of my eyes all the time but I just fail to spot it =)

EDIT: nah, I just compared all of the core module files - the ones I have match identically to the ones shipped with a fresh download of Drupal core. I was hoping for this to be a simple issue like one missing line in one single file :/ well, the bughunt continues =)

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When posting this entry (and the comments), I thought that this will give the non-programmers a glimpse of what bughunting looks like =)