Noticed this too when patching up some addons to get them to work. Basic fix for me was to just inherit from Blizzard's cooldown frame template when creating your cooldown frames.
E.g.
Code:
bar.cooldown = CreateFrame("Cooldown", bname .. "Cooldown", bar.frame, "CooldownFrameTemplate")
Once I did that they started working and I was able to mess around with enabling and disabling the radial edge texture. You can also change the swipe texture if you really want to shake things up:
Code:
Cooldown:SetSwipeTexture("Interface\\Garrison\\Garr_TimerFill-Upgrade")
Haven't really looked if there was a way to change the edge texture or not though.