Description: When a player places any kind of leaves block (with its default block states decayable=false and check_decay=false) and an observer block observing it, the first time a log block is broken 4 or less blocks away from it, the observer block detects an update without any noticeable change on the block state of the leaves block. Further attempts of placing and breaking a log near it, or breaking any existing logs nearby, does not issue any more updates. Log and leaves types do not seem to affect this.
Not easily appreciated in the screenshot, but last particles of the log breaking and redstone activation are still visible.
Steps to reproduce: On any world, place a leaves block directly from creative inventory and an observer block observing it. Then, break a log block 4 or less blocks away from the leaves block, or place a new one within that radius and break it. The first time it is done, the observer block will issue a pulse, but not the next ones for the same leaves block.