New Property not showing in edit mode

Hi there, 

Working on an existing block, 

[Display(Name = "string 1", GroupName = SystemTabNames.Content, Order = 10)]
[CultureSpecific]
public virtual string String 1{ get; set; }

[Display(Name = "string2", GroupName = SystemTabNames.Content, Order = 15)]
[CultureSpecific]
public virtual string string2{ get; set; }

[Display(Name = "string3", GroupName = SystemTabNames.Content, Order = 20)]
[CultureSpecific]
public virtual string string3{ get; set; }

[Display(Name = "bool1", GroupName = SystemTabNames.Content, Order = 25)]
[CultureSpecific]
public virtual bool bool1{ get; set; }

[Display(Name = "bool2", GroupName = SystemTabNames.Content, Order = 30)]
[CultureSpecific]
public virtual bool bool2{ get; set; }

[Display(Name = "NewString", GroupName = SystemTabNames.Content, Order = 35)]
[CultureSpecific]
public virtual string NewString{ get; set; }

For some reason it will just not appear in the CMS / Edit panel, everything else appears but no joy as of yet?  I'm doing nothing differently, its just a string it shouls appear no? 

Any ideas?