Union of unlabled tuple rest args have bad signature help parameter names

[DanielRosenwasser]

function foo(...args: [string, string] | [number, string, string]
) { 
}

foo(/**/)

Expected

foo(args_0: string, args_1: string): void
foo(args_0: number, args_1: string, args_2: string): void

Actual

foo(args: string, args: string): void
foo(args: number, args: string, args: string): void

https://www.typescriptlang.org/v2/play?ts=4.0.0-dev.20200623#code/PQKhFgCgAIWgBALgTwA4FNoG8AUA6AgQwCcBzAZwC5oBtcxYgSwDtSAaaep1gXWgB9azAK4BbAEbpiHLi3acGcngEpoAXgB80AG4B7RgBMAvlFjAoAM2HMAxoka7m0C7t34iZKrVmsZi3gJCYpLSCtzyPqQ8UKpYptAJUCaQlq44AIwATADMbMpAA

[ShuiRuTian]

Sorry for asking.
It has been detailed, but I still could not understand the second one, what is its issue?