Not sure if this is a Foundry issue or a Stacks issue.
If I have two headers of the same type, select them both, and then use custom font size and change the size, the header sizes will not change in preview. If I change them one at a time, the font size change will be reflected in preview.
Not a huge issue, I know, but I thought I should bring it to your attention.
The stack doesn’t have any control over multi-selection changes. If you’re noticing a problem with that you’ll want to file a bug report with Isaiah I think.
thanks for the bug report @dougmon. i’m sure this worked a couple versions ago but it seems i’ve crippled the re-render after properties change on multiple items. even built-in stacks for built-in properties like border on a text stack behaves this way. 
i suspect i introduced this in 4.0.1 – i will investigate. i’ve currently filed it to the bug tracker here. you can sign in and get updates about when this changes.
i’ll definitely get this fixed in the next small update.
Thanks much! This is just a slight inconvenience so far, but I’m sure everyone appreciates your attention to details like this.