Error "The SELECT would examine more than MAX_JOIN_SIZE rows;..."

[zeta77]

I updated to 5.1.0 and received the following error:

Joomla Version Update Status
Notice The update completed with errors.

Brief list of captured errors
The SELECT would examine more than MAX_JOIN_SIZE rows; check your WHERE and use SET SQL_BIG_SELECTS=1 or SET MAX_JOIN_SIZE=# if the SELECT is okay (The update error log gives basically the same info)

Issue# 1: I did use SET SQL_BIG_SELECTS=1 as suggested in several places (also by my host, ONE.COM). However, that does not seem to make the error go away. Is there a better fix?
Issue# 2: I cannot see any problems with the site and my update status is now "green = no update needed". So, do I have to concern myself with this error. If so - what problems should I expect to see?

[Per Yngve Berg]

Did you reapply the patch after the update? The file have been replaced and you patch no longer is present.