Blade Flurry Channeling Speed

The channeling speed for Blade Flurry seems to always take the APS of your main hand weapon, even if that weapon isn't usable by Blade Flurry itself.

Take a slow dagger, with 1.2 to 1.4 APS, and combine it with a Brightbeak with 2.1 APS. Swap the two weapons between your weapon slots as you observe the channeling speed of Blade Flurry. When the Brightbeak is in your main hand, your channeling speed will be much faster (nearly 2x) than when the dagger is in your main hand. It does not average the two weapon speeds or use the APS of the weapon actually doing the attack, only the APS of the main hand weapon itself. The attacks per second listed on the character sheet is inaccurate.

The damage portion of the ability itself still seems to work as people would expect. With the Brightbeak in your main hand and the dagger in your offhand, Blade Flurry would deal damage only from the offhand.

This is true. Also some user tested it here: https://www.reddit.com/r/pathofexile/comments/5drxld/blade_flurry_dual_wield_bug/

Tested: https://youtu.be/tV3uWGk0hco

Displayed APS still changes depending on the off-hand weapon, without any impact on performance of Blade Flurry. It's really annoying. You can't compare APS you had while levelling, using faster off-hand weapon, with APS you have later on, with much more passives and gear, but slower off-hand weapon.

That's a bug with the tooltip system as a whole when dual wielding weapons that are not both compatible with the skill in use. Its not a bug with Blade Flurry.