Steps:

1. Go to Admin/Content Types/Content
2. Click button to create new Content Type
3. Fill Name and Identifier, add for example ezstring (field definition should contain min/max length and default value fields)
4. Fill Miminum length with 10
5. Fill Default value with test and click Save

Actual result:

Content Type is successfully saved. But if you proceed with following steps:
6. Go to edit mode of Content Type
7. Make Minimum length field empty
8. Click Save
an error will be displayed that the string cannot be shorter than 10 characters.

Expected result:

Minimum length and Default value are validate after first saving. When user remove minimum value, content type should be updated without errors.