QGIS simplify geometries shifts polygons north

I'm trying to simplify polygons in a shapefile using the "Simplify Geometries" tool in QGIS 2.10 (Pisa). This works as expected, except for one strange effect: the resulting features (shown in green) are slightly shifted to the north:

How can I avoid this?

As my comment noted, make sure you define your layers CRS before running the Simplify Geometries tool to avoid feature shift.

Watch the video: GIS Solutions - QGIS How to create a polygon, cut it and merge (October 2021).