I'm not sure if this is the same or related to Issue MCPE-26222 or not, or if it is a new intended "feature".

Prior to BTU, when placing items against items with inventories (hoppers, droppers, chests) while flying in creative mode, sneaking (shift+space) would allow you to place the block without opening the object's the inventory AND without losing altitude.

After the BTU official release this no longer seems to be the case and you have to time your block placement before you fall past the area, although the descent is slower it still creates block placement errors often.

Sorry if this is a duplicate, but I did not see any similar issues in the search results..
This is for the official Bedrock release version. I'm also only guessing if it is version 1.2.0.81 as my opening screen only shows 1.2.0