This is really not common and if anything it's something unheard of to me. I work in an English speaking company in Japan and most of my coworkers (who are fluent enough to speak English in technical conversations) would instantly switch back to Japanese to talk about technical things between them if there's no foreigner involved in the conversation. I've seen the same thing happen in my wife's company and other companies too. This is on top of the fact that the level of English education in Japan is very low (unfortunately) and these people who work in English-speaking companies are very much the exception. I don't think I've ever seen a single Japanese person favor using English over Japanese for technical discussions if they were ever given the choice.