Increasing line width changes path

[Kalleheikki Kannisto]

For lack of a better idea, check if you have snap to pixel on, and turn it off if so. Maybe you’re snapping the bounding box to pixel grid every time you change the line weight and this shift accumulates?

[Nick Smith]

Thank you for your hint. It’s indeed somehow connected to the pixel grid snapping. Meanwhile I found the solution here:

https://graphicdesign.stackexchange.com/questions/2644/applying-stroke-to-path-in-illustrator-moves-the-path

Quote: You need to disable “Align to Pixel Grid” in the transform option panel for this path.