That would explain it then. I normally carry my pen in my pocket, i.e. vertical with the nib uppermost, so it might have expelled ink, but would only be so tiny an amount as to be unnoticeable.
I recall for the Fisher Space Pen, that most of the $$$$$ they spent was for the ink, mostly to get the required precise viscosity versus dispensability.
As for the ziploc bag, the only object that gets that treatment is the shampoo, which always makes a bid for freedom, no matter how much I try to squeeze that last bit of air out of the bottle. I wonder when manufacturers will get round to designing a bottle that doesn't leak.
I too have had biros throw a wobbly in airplanes. I wouldn't recommend that as a safe alternative.