I placed a composter on moist farmland next to two separate granite walls. As I did this a villager walked through the space and cancelled placement of the composter, but the walls remained in the low connected state as though the composter were still there.

I expected the walls to remain unconnected or revert to the unconnected state when the composter failed to place.

I'm not sure how to reproduce it without trying to force mobs to move while I'm placing blocks. It may be important to note that visually the composter placed for a split second before it failed.