So, that's what's happened:
I was in route 110 hunting Trubbish. In the meantime, I had my Frisk (and Thief) Furret in 1st position. I find some Voltorb holdin Magnet and I stole it from them, and that was ok.
Then i find a Gulpin holding Big Pearl. I used Thief, but I got no message and no Big Pearl. Some minute after that, it happened again. However, I'm still stealing Magnet from Voltorb..
is that a bug? I'm pretty sure I stole Big Pearl from Gulpin some weeks ago..
ps: I hope that's the right section.