By default, the core engine does not process only buckets that are currently visible. Due to that fact that entities might exceed their bucket seams, the surrounding buckets must be included to the loop update process in order to avoid undesired visual artifacts.
The image below shows how the engine includes border buckets:
If an entity in a yellow bucket exceeds its seams and partially appears in a blue bucket, it will be drawn normally. This feature avoids visual artifacts, since entities won't mysteriously disappear as their buckets are scrolled away.
However, it is possible to disable this feature to boost game performance a little bit, and process only visible buckets:
// Disable border buckets drawing. Set 'true' to enable it again SetBorderBucketsDrawing(false);