Hey Sabatino,
Thanks for reaching out to SmarterTools regarding this issue. I took a look but I didn't see a download link for 120 on their website it looks like they only have 115. Are you also able to replicate this issue on the current public release of Thunderbird?
Thank you,
Zach Sylvester
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com