No, the two calls are dialled concurrently with a skew such that call A finishes dialling moments before call B. Call B immediately goes to voicemail because the line is locked setting up call A. Call A disconnects before the phone starts to ring, but after the network has routed call B to voicemail.

Edit: clarified.

this can then be easily fixed by the networks. Delay the second call request until the first call actually rings.