It's not just a tooltip error, because it's been tested on the character window as well. So either there's a 1% DR bug, or a bug with stat-reporting in the character window --- either of which is an important bug to fix. Yes, several of us have filed a bug report. :-)
1% is small enough to be difficult to confirm without a lot of parsing effort, given that most damage abilities have a range over which they hit. If anybody knows an ability that hits for a constant amount of internal/elemental damage, please let me know, and I'll go check. But since I don't know of any such, It's reasonable to ask the devs: "What's up with this?"
Edit: Someone suggested the fires on Dromund Kaas, but these seem to be energy damage; they are mitigated by armor.