There is no entry in the dewiki database.
mysql> select * from ipblocks where ipb_address = '137.226.39.166';
Empty set (0.44 sec)

It is in the logging table.

mysql> select count(*) from logging where (log_id > 18288 and log_id < 23772 or log_id > 77698 and log_id < 99000 or log_id > 226000 and log_id < 290000) and log_namespace = 2 and log_type = 'block' and log_title = '137.226.39.166';

> 17

This looks like an isolated case.
See
http://de.wikipedia.org/w/api.php?action=query&list=blocks&bkusers=212.117.127.28&format=xml
http://de.wikipedia.org/w/index.php?title=Spezial:Logbuch&type=block&page=Benutzer%3A212.117.127.28

http://de.wikipedia.org/w/api.php?action=query&list=blocks&bkusers=193.171.250.98&format=xml
http://de.wikipedia.org/w/index.php?title=Spezial:Logbuch&type=block&page=Benutzer%3A193.171.250.98

And earlier on ENWP
http://en.wikipedia.org/w/api.php?action=query&list=blocks&bkusers=212.211.136.33&format=xml
https://secure.wikimedia.org/wikipedia/en/wiki/Special:Block/212.211.136.33

Have you tried to unblock it and reblock it?

If you want to check that there are no other missing blocks, compare the logging table with the ipblocks table.

Here's another one from de.wp:
https://de.wikipedia.org/wiki/Spezial:Liste_der_Sperren?wpTarget=203.160.1.146&limit=50&wpFormIdentifier=blocklist
https://de.wikipedia.org/w/api.php?action=query&list=blocks&bkusers=203.160.1.146
https://de.wikipedia.org/w/index.php?title=Spezial%3ALogbuch&type=block&user=&page=203.160.1.146

I made a series of ip unblockings back in 2013. Probably they did not compute well to database?