While flying in creative mode, you can no longer press SHIFT while holding the SPACE bar to stop going up or down. Instead, it causes you to move down, though at a slower speed than pressing SHIFT alone.

This causes a problem when you're trying to place a block against another block that has a USE interaction, since the only way I know of to avoid invoking the USE interaction is to hold SHIFT while you right click to place the block. If the block you want to place against is up in the air, it's tricky to place the new block while you're descending. This is especially inconvenient for redstone components such as hoppers and repeaters where you have to click the block you want its output to face.

The changelog for build 9 included a fix description "Drift has been reduced in creative flight mode and players won't drop out of flight by touching the ground." While I like not dropping out of flight mode any more, I suspect that that fix introduced this problem. If I had to choose, I'd rather have it the way it used to be because the changed mechanic is making my redstone builds a lot more difficult.

Steps to reproduce:
1. Place a hopper, dropper, or any other block that has a USE interaction.
2. Enter creative mode and start flying.
3. Attempt to place redstone dust, a slab, a trapdoor, etc. against the block by holding down SHIFT and SPACE together while right clicking. Notice that you are moving downward as you're doing this.

Incidentally, it is still possible to press A, S, or D while holding SHIFT and SPACE to move sideways or backwards, but pressing W to move forward has never worked for some reason. It would be nice if you could because it would make it easier to, for example, add stairs to the edge of a roof if you didn't have to do it while flying backwards.