Accessing the item from a button shows strange results. For an alert, it works but sometimes shows undefined. As you can see in the following screenshot under description, the item.plate is red but under "Only run when" item.type is green and defined.
We recently pushed a fix that should allow for item to be used in script event handlers! Can you let me know if you're still seeing other behavior?
The second issue you mentioned (item being available in the "Show row" field) is still being investigated. Does the workaround you have there work for now?