Docker Images disappearing on Windows

Expected behavior

My previously created images remain on the Docker Host when I reboot my laptop.

Actual behavior

All Docker images are gone after a number of images are created. The images are 1gb or more in size.


Windows 8
Docker Toolbox 1.8.2c


How do I investigate what the problem is?
I am actually guessing that at some point I have too many large images, but I cannot confirm.