My students are all using Chromebooks. We have Lenovo N22 Chromebooks. I’ve tested this on my own machine - Windows 10, and I see the same issue.
I just tried re-creating it. The first few times, it seemed to switch after drawing the first or second rectangle. Now, it happens after drawing anywhere from 9 to 20 rectangles sequentially. I double checked to make sure that I’m not hitting the CTRL key.
Here’s my chrome version:
||70.0.3538.77 (Official Build) (64-bit) (cohort: Stable)
||Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36