SBJsonParser in iPhone App

I am working with the JSON library and see this situation:

Convert JSON string to NSDictionary

Scenario 1:

NSString *jsonString = @"{\"Name\":\"Foo\", Points:5}";
NSDictionary *dictionary = (NSDictionary*)[jsonParser objectWithString:jsonString];
NSLog(@"Dictionary: %@",dictionary);

I see the result as follows:

Dictionary: {Name = "Foo"; Points = 5; }

So right.

Scenario 2:

NSString *jsonString = @"{\"Name\":\"Foo\", Points:0.5}";
NSDictionary *dictionary = (NSDictionary*)[jsonParser objectWithString:jsonString];
NSLog(@"Dictionary: %@",dictionary);

I see the result as follows:

Dictionary: {Name = "Foo"; Dots = "0.5"; } ???

Scenario 3:

NSString *jsonString = @"{\"Name\":\"Foo\", Points:-1}";
NSDictionary *dictionary = (NSDictionary*)[jsonParser objectWithString:jsonString];
NSLog(@"Dictionary: %@",dictionary);

I see the result as follows:

Dictionary: {Name = "Foo"; Points = "-1"; } ???

Why does the JSON library convert negative numbers or a number less than 1 into a string? Do you know how to prevent this?