No scrollbar if textbox has alignment set to bottom

I'm embedding an AI chatbot solution into my storyline, and while I've managed to surpass so many hurdles, I'm stuck on one last thing.

To make it function like a chat, I have a textbox aligned to the bottom. This means new text appended to the variable make the text 'scroll up'. This works fine until the textbox is full - and while it keeps appending the text, no scroll bars appear.

If I set the alignment to 'top', then it works and I get scroll bars, but then I have the issue of not automatically scrolling down. 

I feel like the scrollbars not appearing when alignment is set to bottom could be a bug? thoughts?