MYSQL - 'Select distinct' - different results on two exact versions of Mysql, databases synced
This is just a hunch, but make sure your collation settings are the same between the dbs.  I know you said they're synced, but check.

If you can't find anything there run each select into their own outfile 

select bdtag3_.* into outfile '/tmp/db1.data' ....


and

select bdtag3_.* into outfile '/tmp/db2.data' ....


You have an order by so running a basic commandline diff should quickly highlight differences.

The pt-table-checksum tool is also handy for finding differences.