The story
From keybed + -ing. Coined by Tobias Matthay (see quotations below).
Etymology from Wiktionary, CC BY-SA 4.0.
keybedding
Today it means: The fault of continuing to press down too hard on the keys of a keyboard instrument after the initial key depression that creates the sound, thus holding the keys against the keybed with excessive force beyond that needed to produce the sound and keep the keys from rising. Full definition →