They've been flipping materials since day 1. Are they flipping differently these days ? I doubt it. Mostly the high prices that persist seem to herbs which makes sense since that where the most consumables lie. That said the thing that I think has changed is we no longer have the over-supply of mats* that we had before Legion due to the huge amounts required to make items.
*The lack of Zin'athid and Osemite nodes exacerbates is an addition problem.