Inventing a hole

Read the following story that may or may not be true. I liked it:

A Danish inventor was asked by a bank to invent some kind of mechanism on their piggybanks that would prevent the money put on the piggybank to fall out through vigorous shaking. Indeed he invented the right mechanism. The inventor got paid a good sum of money for his invention.

Personal memory: I remember the frustration back around 1960, when I discovered the money would not come out.....

After some time, the clients reported to the bank that as far as keeping the coins in, the invention was great, but the bank notes often got stuck in the mechanism. They offered to pay the inventor the same sum of money if he could find a solution for the bank notes.
The new invention was extremely simple and smart: A simple hole, smaller than a pencil, enabled you to push in a rolled up bank note, but made it impossible to take out!

Personal memory: I also remembered that little whole on the side of the piggybank.