Hi ORE,
Yes, this is unwanted behavior.
Anyway I have created a temporary solution which resolves the issue.
Just add the following CSS snippet:

.smart-tabs[vertical] .smart-tabs-content-section,
.smart-tabs[vertical] .smart-tabs-header-items{
    height: auto;
}

Let me know if that works for you!
Please, do not hesitate to contact us if you have any additional questions.
Best regards,
Yavor Dashev
Smart UI Team
https://www.htmlelements.com/