After reading this I went and did some analyzing of our logs. I can confirm that Blade Flurry damage is being halved on the same colored twin.
Code:
[20:56:43.694] Vegil Eviscerate Fjola Lightbane *17762*
[20:56:43.709] Vegil crits Fjola Lightbane *5239*
[20:56:44.413] Vegil Eviscerate Fjola Lightbane 2098
[20:56:44.803] Vegil crits Fjola Lightbane *5518*
[20:56:45.022] Vegil hits Fjola Lightbane 799
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[20:56:44.366] Vegil Blade Flurry Eydis Darkbane 8881
[20:56:44.709] Vegil Blade Flurry Eydis Darkbane 2620
[20:56:45.100] Vegil Blade Flurry Eydis Darkbane 1049
[20:56:45.772] Vegil's Blade Flurry fades
[20:56:45.928] Vegil Blade Flurry Eydis Darkbane 2759
[20:56:45.928] Vegil Blade Flurry Eydis Darkbane 399
This was the best example of non-absorbed blade flurry damage I could find to illustrate the proof. You can clearly see the huge initial crit and the following hits, ending with a much smaller hit, all being halved on the other twin.