Thanks for reporting this Canarsie.

As I understand it, this is a known, and as yet, unresolved issue. Luckily, as you noted, it only occurs intermittently, and the issue is relegated to exceptionally long threads. vBulletin handles these long threads better than our previous bb software (with UBB we had to manually segment long threads into multiple threads), but it obviously doesn't handle them well in every case.

I've passed your report along to the IB tech team as another data point.