check.tp.o do not handle IPv6 properly
check.torproject.org currently resolves to an IPv6 address on top of its IPv4:
check.torproject.org is an alias for sergii.torproject.org. sergii.torproject.org has address 220.127.116.11 sergii.torproject.org has IPv6 address 2620:0:6b0:b:250:56ff:fe99:61
Unfortunately, the code behind https://check.torproject.org/ does not seem to handle IPv6 connections properly as it currently says:
Sorry, your query failed or an unexpected response was received. A temporary service outage prevents us from determining if your source IP address is a Tor node. Additional information: Your IP address appears to be: 2001:9...
No harm done, as the negative answer is correct, but it does not look like an optimal answer.