Still getting "Invalid Entity Filter" and "Invalid Filter"

When doing a "drush cc" I get the "Invalid Entity Filter" and "Invalid Filter" messages and have to refresh the page a few times before they go away. (See CRM-18504). 

I also see them in the logs sometimes.

I found this advice: https://issues.civicrm.org/jira/browse/CRM-18504?focusedCommentId=100018&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-100018 and discovered that I had an empty-string value in civicrm_custom_group.extends_entity_column_value. The advice said to change it to an integer (in this case would be the relationship type id) but I looked at the other values in the table and they looked like 
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for example where the characters on each side are the MySQL representation of a binary value, you know the box with ones and zeros in it. So I took a value from a different field, replaced the integer inside it with the desired relationship type id and updated it to that. It updated but gave me many warnings - one for each row (although I was only changing one row) saying "Truncated incorrect DOUBLE value". Which is odd because the field is not a double but a varchar. It made no difference - the next time I did "drush cc" the error came back again.

If someone could shed light on what these binary things on either side of the value are, that would be great.