This is a persistent issue, and always has been, for those that navigate the editor via holding alt + LMB (rotate cam) or alt + RMB (zoom cam). For those using RMB + WASD to navigate, this can still be an issue as the RMB menu does pop up upon release of RMB. For people who prefer to navigate via Maya controls, holding alt to rotate/zoom/pan, UE4 doesnt honor the ‘alt’ button as a ‘camera only’ designation - while holding alt, mesh can still be selected and RMB zoom periodically opens the right click menu when RMB is released. This has always been issue so I assume this is working as intended (unfortunately).