If you use a command block to issue a /clone command whose destination includes a block being watched by an observer, the observer usually detects a change and outputs a signal. (This occurs even if the command didn't clone any blocks, or if the destination block contained air both before and after the command; this is reported as the related issue MCPE-52581.) However, if the observer is in a different chunk from the destination block, it does not detect a change even if the command actually replaced the original block with a different one.

The attached world demonstrates this issue. A square of quartz blocks identifies the interior of a chunk. The chunk contains 5 cross-shaped devices, each with an associated command block. One cross is in the center, the others are at the corners of the chunk. When activated, the command block clones a diamond block into the center of the cross. The arms of the cross consist of observers watching the center and redstone lamps to make it easily visible which observers output a signal.

Steps to reproduce:

1. Open the attached world.
2. While watching the redstone lamps, press the button on one of the command blocks.

Expected results:
The clone command places a diamond block in the center of the cross, triggering a detection in each observer, which activates all four redstone lamps.
Actual results:
Only the device in the center acts as expected. For the devices in the chunk corners, the clone command apparently only triggers the observers that are in the highlighted chunk. If you manually place or break the block in the center of the cross, all four observers are triggered as expected.