Spring Web Flow JSR 303 Annotation based Validation

I am trying to do JSR 303 annotation based validation in the spring web flow module in my project but i read that the error messages in the messages.properties should be defined as

{command-object-name}.{attribute-name}.{constraint-name}=My Error Message Text

Example

name.Size = Name should be between 1 and 100.

but

Size.name doesn't work for Spring Web Flow where as both ways

name.Size as well as Size.name work for Spring MVC

Can someone explain me why is it working?