I believe this effect does count towards the worn FT15 and worn 250atk caps. I believe there are no items in EQ which do not obey these cap rules. These caps are fundamental in Sony's plan for "class balancing". Occasionally SoE makes a mistake as was the case with the Coldain Prawyer Shawl for a while, but even that was corrected some time ago.
Doughnutman Feral Lord Doughnutmezz Coercer [link=www.landslide-guild.com]Landlside[/link] of Ayonae Ro
Flowing Thought, or mana regen + as it is now known, falls in the same category as any and all >>> worn <<< mana regen. This is the same for any >>> worn <<< + attack items, formerly known as Vengence items. Anything that gives a + mana regeneration or flowing thought effect counts towards your worn mana regen cap of 15. Again, same thing with Vengence/+ attack items.
Now, there are items that have right click buffs that may or may not stack with other buffs of mana regeration or attack bonuses. These items do not count towards the worn boonus as they provide buff icon and take up one of the 15 buff slots that are available to you. Also, usually, but not always there is some limiting factor to these buffs that extend your mana regen and/or attack beyond the usual Avatar/kei/VoQ line. They are some times temporary buffs lasting less than one minute. Other times they have a "rune" type effect which means when you take damage once the "rune" portion of the buff have been used in absorbing the damage they fade and must be recast.
Hope that answer anyone's questions about "worn" + attack / + mana regeneration vs. buff clickbale + attack / + mana regeneraton items.
The Avatar Proc of Primal Weapons (Ancient Prismatic Weapons) from Sleepers Tomb does count to the worn ATK cap but is a buff slot. The Avatar/Primal Avatar cast by shamans does not count to the worn cap.