Duplicate Declaration error for flow type declaration

Hi

If I have the following:

// @flow
export class WhatsWrongWithThis {
    example1  : (string, string)=>void; // doesn't like this
    
    example2  : (param1: string, param2: string)=>void; // but this is fine
    example3  : (string, boolean)=>void; // also fine
    
    example4  : (string, boolean, string)=>void; // doesn't like this either
}

then the 2 string types in example1 and example 4 are highlighted with a "Duplicate Declaration" inspection error. Doesn't seem wrong to me though, what am I missing? I'm on Webstorm 2019.1 EAP (on a mac)