On the Variabled tab:
The Disk icon and the green + icon actions are swapped.
When you click on the green + icon, the window that pops up is titled Variable Save, and asks if you want to save the current variable.
When you click on the disk icon, the window that pops up is titled New Variable, and asks you to enter the name for a new variable.
Thanks for the report. Do you mind reporting it as an issue on Toucan's github: https://github.com/PortableApps/Toucan/issues, so that I can track it to closure?