In the current version of Editorial (1.1), the iPhone workflow editor crashes when you try to insert a variable in a single-line text field (e.g. the title of a Show Alert action). This doesn't happen in the iPad version, and it only affects single-line text fields (which are not very common in the built-in actions).
Here's a quick workaround until I manage to get a bugfix update ready:
Instead of using the Variable... menu, simply type
%var:<name> in the text field, for example
%var:Input. When you close and re-open the action, it'll show the variable name as a blue placeholder.