I have created a modal that works in moving the model from the modal to the form, however if the field has required: true, the form will not validate if the field is touched but then checked in the modal.
I have a working JSBin showing the issue.
As you can see from the example, I have tried various things to force the field to valid without any luck.
Any help would be appreciated.
No idea why you are moving the model to a modal and then back, it seems to serve little purpose. I have found cases when validation doesn't always work right, this seems to be one of them. You have two options. Use an expression property to check a separate flag you set when you select the field to change required to false or simply set a flag and use that to check validation manually.