Sculpt mode: Masking selects more than wanted

I am trying to mask part of a structure in Blender.
However, when doing so, seemingly unrelated parts of the structure are also selected.

I attached a video for illustration and the blender file for testing.

I hope you can help me fix this issue!
Thank you so much!

sculpt_selection.blend (960.6 KB)

Look down in the toolbar there is a syemetry option for an axis checked, unset it, should slove.

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ah - thank you. It was still to early in the morning :smiley: