Same situation. I've read the 1994 immi act that in volume 5, chapter 887.212 (see the attached picture), and it mentions the bridging visa related to skilled visa like 489 is Ok. In my case, I've held the 485 working visa and applied for 489 visa in Oct 2017 and a bridging visa had been granted then. So I was holding the 485 and a bridging visa related to 489 at the same time. I plan to apply for 887 visa in Oct 2019 (2 yrs living and working). Will share with you guys in later this year and 2020 when I get some reply from the CO.