When using the clone command in command blocks the area can officially not overlap. But this is possible when the command block is on the edge of the clone area. In the case of the command block being on always active the command block will now indefinitely duplicate itself until the world-border is reached.

The issue should be repeatable using the screenshots.

This is an issue because when building large structures or farms the clone command is really important and People can accidentele ruin their build because a command block indefinitely duplicated itself and a wall.