Chances are your Mac is an old one that does not handle large textures well. P-P, along with other OpenGL programs that try to use large textures, has problems on versions of OSX prior to 10.6. P-P has adjustable texture size limits that can be set to make it work on almost any platform; but it can't set them automatically. So try this:
Start P-P and click ? then 'tune image size limits'. Click 'test' next to the cube face limit and see what happens. P-P will try to display the test cube image at the specified size. If the cube face limit is too high you will see an incorrect display and/or get an error message about 'incomplete frame buffer'. If so, reduce the limit and try again (however you may have to restart the program first, to get rid of bad OpenGL state). Once you you get a proper cube display, click 'test' next to the flat size % box, and proceed similarly -- this shows the front face of the test cube as a flat texture, which is how P-P shows equirects at present. When the flat test works, your equirect should display right.
Unfortunately this workaround also limits the resolution of saved views. Unlike Panini, Panini-Pro saves at the full resolution of the loaded texture, independent of window size. But it does not yet process images tile-wise, which eventually will allow saving at full source resolution regardless of system limits on texture size.
I see from the screen shot that P-P reduced your image to 12 Mpix, so the cube face limit is already only about 2450. On recent platforms with decent video cards, the limit should be around 3250 (63.5 Mpix) and it can be 4000 or more, approaching 100 Mpix, on a 'gaming' machine. But ultimately I must make P-P handle hardware limitations automatically without any such kluges.