Some people in this thread have expressed reservations about how the YC61 collapses to mono, so here's a bit of Brahms played in mono via L/mono, L only (by also inserting a dummy adapter into the R jack), and R only. Not in that order.
The three recordings use the same MIDI file (also recorded on the YC61), so they are identical note for note. The sound is CFX piano with damper resonance and reverb. I have attempted to normalize the volume, but the recordings still don't quite sound equally loud, so try to ignore pure volume differences.
You can try to guess the order of the recordings. Here's the answer:
Link to recording: https://vocaroo.com/1nATtSfoNXDz Unfortunately I couldn't include it as attachment because of some permission error. Hosting the file on Vocaroo may have degraded the recording, but it shouldn't affect any phasing issues.