The blocking is done based on the filter list. Sounds like one of the included (and enabled by default) filter lists in uBO is causing issues. Did you try disa

The blocking is done based on the filter list. Sounds like one of the included (and enabled by default) filter lists in uBO is causing issues. Did you try disabling all uBO filters to see if the issue persists? If you can narrow it down to a specific filter list you can find the rule that is causing the issue and either disable that one rule or, better, raise a bug report so someone can look into what's going on and fix it in the filter list proper.