The problem is in DataModel wrapper for 'myList'. Wrapper is creating after instance of class has been initialized.
Class instance is creating after first value expression referenced to the bean name. It occurs in dataTable tag,
But Columns requires the model early - during the tag creating phase.
To solve the problem just remove DataModel wrapper, add setter/getters for 'myList' add use it as bean's property on the page.
Anyway columns 3.2.0 version is not stable and contains many issues.
Try the latest version for your purpose.