I just ran a test again where I opened the plugin, chose another preset, verified that the sound changed, closed the plugin UI, saved the Song, and exited Cantabile.
I then re-opened Cantabile and loaded the same song. I opened the plugin GUI, noted that the name of the preset displayed in the plugin's window was the one I selected, but the sound was definitely not. (I purposely chose a sound very different that the Matrix Softstrings II.) Also, as Dave noted, the NUMBER displayed in the "LED window" showed 1, not the NUMBER of my selected preset.
I also verified that the only OP-X plugin in my plugins path was the special 1.2.2 64-bit Cantabile version and that this was the version that was loaded each time.