Astonishing 3D printer problem

[fujitora20]

When I print models with internal top layers, the size of the model externally in the X-Y dimensions grows by 10-15% on the next layer. Things without an internal top layer (that is, objects with top layers above all walls) are not affected. Because the problem happens in both X and Y directions, it isn't a layer shift. This happens on all of the objects I've printed with walls above some of the upper layers, although it's more evident on circular shapes than squares (although noticeable on something like a Benchy, which has an object size increase above the deck on the outside walls of the boat). It doesn't happen at the same time or at the same height every time.

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