The inter-tunings (see inter-languages), which especially occur on a piano or other harp-based instruments (and more so on piano because of the multiple strings per keys), are interesting semi-aleatoric/environmental tunings which would likely be hard to replicate or analyze. Luckily for this one, I sampled the piano so I can have a near-copy at some point.
Since, in this case, the piano was being tuned from a 15-equal drop tuning/slack tuning (from my album: The Devil) because to standard 12 equal, the tension-re-adjustment took a good deal of time. It wasn't/isn't reasonable to think I could tune the piano fully back in a session. I can even hear the piano creaking in the nights, especially as the temperature change, and I can hear where the strings resolved to the next time I play it. Fortunately, I enjoy these inter-tunings a lot. This one was especially cool cause I had tuned the middle few octaves in the C diatonic scale, to something akin to a pythagorean scale but with juster major third -- this is my first time actually tuning a piano to 12-equal by ear, so I hope I can get the tempering good. The rest of the notes were in left-over positions from the previous tuning, or had detuned themselves they were relaxing back into position. Hence, there were various keys which would play multiple notes, various quarter-tone-esque intervals (I need to check my reference pitch again so I don't tune the piano a semi-tone flat), and various large steps and unequal octaves, and even higher keys which would trigger a lower pitch.
My enjoyment of playing keyboard instruments in which I don't know which pitch is mapped to which key will likely manifest more fully in future works, exploring a few ideas such as: the extent of the randomness -- are pitches in sequential order (in this case generally yes, but not always), is it an equal or near-equal tuning / can chord shapes be modulated, does the same key produce the same pitch each time. And how do these effect the spontaneous composition / improvisation of a performer, and how is it related to their musical training / experience (in relation to microtonality, tonality, tradition of music, symmetry, etc) and natural harmonic properties of the instrument / tuning.