This has been discussed in another topic and the answer is that without sync being enabled, there is no "target" tempo to which to stretch the entire waveform in order to display them both moving at the same relative speed. If you played both tracks at 0%, they'd both move at the same speed but the beats wouldn't align. As you likely have one of them pitched up or down to match the other track, it displays that waveform moving faster or slower than the other waveform, with the beats meeting at the middle (think of that as the "play head").
Unfortunately there will be no update to address this functionality, and I will point out that Serato does the exact same thing when using CDJs as your control interface, so the RX isn't the only waveform display to exhibit this behaviour.