I can also attest to this function issue. HyperSnap will not capture a growable textarea form attribute.
For example, I do not have a smart phone-- I still use my ancient LG8300 flip phone. When I need to send lengthy text messages, I don't use the phone. Instead, I use the "Send Text" page on the Verizon website. This is where HS (all versions) fail. Under no options, whether using HS6, HS7 or HS8 can I capture the entire chat dialogue window as it will never scroll that window but instead scroll the page regardless of the option selected.
This is true using the following:
HS6 and HS7 via Firefox 52.x.x ESR under Windows Vista 32-bit.
HS6, HS7 and HS8 via all Firefox versions to current running on Windows 8.1 and 10.0 64-bit (32/64).
In short, no version of HS is able to capture the chat dialogue window on this page, as well as similar pages elsewhere. I'm not sure if this pertains to strictly HTML 5 or earlier HTML 3 - 4 versions, but there was once a time I believe we did have this functionality using HS7-- but I can't be certain because, well, you know my personal history (number 1) and (number 2) during that time I had other screen capture applications running on all 3 machines and don't honestly recall which of the 3 computers it worked with, or even if it was, in fact a HS version that ever performed this function properly. Which is most probably the reason I have other screen capture software installed. Because as you know, HS has always been my primary (and for a decade, only) screen capture program installed on any machine. And I've been using HS since 1999, the last version of HS3! Which is probably the time I was most active on the old, original boards.
But anyway, when I come across a public page to use as an example, I will post it here. Meanwhile, if anyone has Verizon cell service, you can test it out here: https://web.vma.vzw.com/vma/web2/Message.do
Send a lengthy text message that comprises over 500 characters to ensure the growable textarea, then click on your sent message. Try to capture just that message using HS. You will find that you cannot. HS will not capture a growable text area and that's the issue.