This is actually a feature and configurable setting that was added with the ability to print single extrusion walls. This is the function of end point extrusion distance. If you lower this setting to 0 you won't see any added extrusion to help the single extrusions meld better with the surrounding part. If you raise it, you'll see an even further extension. Have you printed these parts yet? Are you seeing issues with the extrusions being too far? If so, you can try lowering the endpoint extension distance a bit.
More on using these features: https://www.simplify3d.com/support/arti ... -features/
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