I've not tried IPv6 with TWS, but I wonder if internally there's a matching issue with the :0:0:0: portion of the address. What I mean is, IPv6 allows skipping the 0s and rewriting that portion as :::. When you entered the trusted address, did you use the 0s or skip them? I'd try it both ways and see if one works. Just a guess. It seems like a plausible bug if they're doing string based matching they may be stripping (or inserting) in one place, but not the other.