Can't erase shape keyframes on frame 0 (solved!)

[Reindeer]

Let's see if I can explain the problem I've just bumped into. I'm designing a character. He hasn't been rigged yet, it's just plain graphics and layers.
I've been playing around just doing some point-animation to test whether certain facial expressions will work once I'll get 'round to rigging.
Today I reopened the file, erased all the point keyframes on the timeline (point position, curvature and line width, T, C and W tools), but the original shape now has a keyframe on frame 0, and it can't be erased. It's as if the original shape has been modified in some permanent way.
I chose "Erase all animation from document", to be sure this caused by some keyframe on some very distant frame on the timeline, but no-go. Some layers now seem to have default "0" keyframed curvature, motion and width values.

EDIT: JUST FOUND ANSWER...! By going to the Animation menu and then choosing "select all keyframes" and then deleting, the keyframes on frame 0 disappear.
Why this didn't happen when I repeatedly selected said keyframe (after having previously made sure there weren't other keyframes on the timeline conditioning it), I have no idea. Somehow Moho likes this selection and deletion better

[Greenlaw]

I haven't seen that one in a while but what I do is I create a keyframe a few frames into the timeline, copy that keyframe, and then paste it into frame zero. Then I'm able to delete both keyframes.

Not sure why that works but it somehow it informs Moho that there's a keyframe there.