Error reading the Fields of a class using Reflection

I have a very strange case decompiling a class.

The class has this three fields:

private String descError;
private Number codError;
private List<String> errorList;

When I decompile the class with FernFlower or JDGui I can see the three fields with no problem, but when I load the .jar containing the class into my classLoader, this class has a "Map" instead of a "List".

I obtain a :

java.lang.reflect.Field

With this properties:

Signature: Ljava/util/Map<Ljava/lang/Object;Ljava/lang/Object;>;

Type: interface java.util.Map

class: Myclass

Anyone knows what can be the cause of this strange case?