Question about Markslöjd Multi

I may present the solution myself: It is because Galaxus initially recommended the 'Eglo Vintage Amber (E27, 330lm, 4W)' for this luminaire, but it is not dimmable. It works with a dimmable LED bulb.

So it works with a conventional light bulb. It must then be residual current that the LED bulb "utilises".