Hey!
Many Apologies, That is a serious issue and one that I have gone ahead and fixed immediately. If you go to the download page, you will now see 0.6.1(experimental). This version should be able to export the thumb no problem, I just tested the fix in Cura. Please note I was in the middle of working on a new independent base width feature that is included but relatively untested in this fix. If you encounter any further issues, please do let me know.
Thank you so much for your support!