Thank you for your answer jcl!
Sorry, thats not actually a quote, I just put the core sentence of my question into a box for better visibility. It is just a fact about Zorro that I observed experimentally.

EDIT:

Indeed, IB calls this concept "Equity with Loan". Am I the only one who thinks that this is a gold mine? Never sell any decent asset ever again! Just buy new ones on Equity won!
Here is a picture from their website: