Right channel only working with additional set of earphones plugged in

Hello everyone!

Can’t figure out what’s happening with this (really cheap) headphones I have.

This is the model http://offers.kd2.org/en/gb/lidl/pkNC/

The cable goes into the Left speaker and there over to the Right one. Then in the R earpiece there’s a connector where you can plug in an additional set of earphones.

So, my problem is the R speaker won’t emit any sound UNLESS i plug another jack into this additional connection. Then both speaker works and also the second piece of earphone.

What’s puzzling is that it not just any jack will make it work. it actually works only with one of the many ones I have tried. It’s a set of earphones with mic, so a 3 stripes jack (tip-ring-ring-sleeve). But I’ve tried several other sets, with both 2-stripes and 3-strips and it won’t work. I don’t understand what’s special about this one…

Here is a photo of the R earpiece opened up.

Thanks for any suggestions!

ps. with any other set of earphones, only the L speaker works and also only the L channel of the addition set of earphone