I have a similar story about our child, at a similar age! He waited until I'd left the room before dragging a chair away from the dining table and then climbing it, in order to reach a toy I'd accidentally placed on a high shelf on the book-case.

When I came back he immediately knew he'd been caught. Though I wasn't at all mad, it was a wakeup-call that from then on placing things too high was probably a challenge for him, rather than an absolute protection.