This is just a matter of WhoIs stripping off the host part of the query and only sending the "yp.to" part. Tonic WhoIs returns for that:
joe@debbie:~$ whois yp.to Tonic whoisd V1.1 yp uz5jmyqz3gz2bhnuzg0rr0cml9u8pntyhn2jhtqn04yt3sm5h235c1.yp.to yp uz5jmyqz3gz2bhnuzg0rr0cml9u8pntyhn2jhtqn04yt3sm5h235c1.ns.yp.to
WhoIs Lookup performed by Karen's WhoIs v2.7 Visit https://www.karenware.com/ Query [testnameinvalid.yp.to] whois://whois.tonic.to
Source code for Directory Printer v5.4.2 posted on https://www.karenware.com/powertools/karens-directory-printer
Source code for Replicator v3.7.4 posted on https://www.karenware.com/powertools/karens-replicator-backup-utility
Did not actually rebuild the RIR database because Karen's original source from MIT isn't still available. I could rebuild the file from less convenient sources, but enabling recursive queries through whois.arin.net fixed the operational situation.
Version 2.3: Updated TLD table to reflect new WhoIs database authority for .org TLDs. Also improved program's handling of reponses from WhoIs servers that consist of multiple data packets. Program also accepts a domain name or IP address passed via its command line, to accomodate new feature added to Karen's URL Discombobulator.
WhoIs Lookup performed by Karen's WhoIs v2.7 Visit https://www.karenware.com/ Query [2607:f8b0:4009:816::200e] whois://whois.arin.net
Forced use of first whois server on IP Address lookups.
Fixed for Domain and IP queries.
Setting Focus and Default