Hot answers tagged meta-query
NO, you cannot combine post_in and post_not_in in the same query. Both are mutually exclusive, So it is impossible for mutually exclusive events to occur at the same time.
The problem is with the arg 'meta_key' => 'meta_value' - meta_key isn't needed if you have a meta_query arg (despite what the codex appears to say) and its value here doesn't make sense anyway - so just remove it. However it does point out a behavioural change in 4.1 as before the meta_key was ORed with the meta_query keys (hence your query worked as the ...
Nested relations among subset of meta queries are possible on WP 4.1 that is planned to be releaded next coming December 10, 2014. See trac ticket. So wait a few days or use the beta version.
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