Designer Task Data Assignments and Commas

We are using a recent snapshot of 2.2 process designer.

I have a task with an attribute that is taking email addresses as values, I enter the value in the To Value column of the Editor for Data Assignments window.

If this is a regular email address then this works fine, but if I want to list email addresses delimited with a comma (so I can put the addresses into a recipient list in an email) the editor seems to accept the values, but on reopening the Data Assignments window the second email address is treated as the "From Object" in the attribute underneath. I guess that the comma is being used internally to Designer, and not being escaped.