after merging https://github.com/Behat/MinkSelenium2Driver/pull/123 the event count went down from 2 to 0, because the field was not unfocused anymore (looks like applying Syn forced the unfocus) and so the native event was not triggered either.
Well searching on Google about the issue, I found a tip about putting a TAB at the end of the keys being sent, and it indeed works.