Had an issue come to me yesterday where a category page couldn't be saved. Basically, the user was trying to update their meta keywords on the seo tab and went beyond the 400 character limit.
Property: MetaKeywords Error: The field MetaKeywords must be a string or array type with a maximum length of '400' is the error thrown...however, the user gets the white "error screen" and they don't know what happened.
I look at this as a bug as the validator isn't firing properly.
Visual Studio dumps
[DbEntityValidationException: Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.]
System.Data.Entity.Internal.InternalContext.SaveChanges() +182
System.Data.Entity.Internal.LazyInternalContext.SaveChanges() +56
System.Data.Entity.DbContext.SaveChanges() +52
Nop.Data.EfRepository`1.Insert(T entity) in e:\Development\NopCommerce\Libraries\Nop.Data\EfRepository.cs:52
[Exception: Property: MetaKeywords Error: The field MetaKeywords must be a string or array type with a maximum length of '400'.
]
Nop.Data.EfRepository`1.Insert(T entity) in e:\Development\NopCommerce\Libraries\Nop.Data\EfRepository.cs:64
Nop.Services.Logging.DefaultLogger.InsertLog(LogLevel logLevel, String shortMessage, String fullMessage, Customer customer) in e:\Development\NopCommerce\Libraries\Nop.Services\Logging\DefaultLogger.cs:197
etc....