Hi Bob,
The way you have set up the domain model validation should work the way you expect, so there are a few things to check to get more details about what is wrong.
1) After you enter incorrect details, are you hitting a 'save' button in your app? If so, does that Save button trigger a custom microflow? The validations entered will only be triggered when you try to commit those entities.
2) When does the form disappear? Is it happening right after you leave the field with the entered data?
3) Are there any errors in your console?
Nothing jumps out as being obviously wrong here. Can you post a screenshot or two?