Currently Qtranslate and WPML translate are the translate plugins officially supported, others might cause issues, although they usually work without issues. I cannot promise it's going to work correctly with this one.
However I did a debugging on the queries, and they are doing exactly what you described. The first one looks in the title, content etc.. but not in that custom field, and the other one looks only that custom field. It's 100% correct and working. What is the problem exactly? The results must be the correct items, as the query is correct. Is there something with the language?Best,
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