This is the cause:
bitcoin:12WWoWbnNCPcGegxvkcgvMEKfsm1VfjJda?amount=5.149e-05&message=Cuz%20my%20random%20babbling%20is%20worth%20half%20a%20two%20cents%20worth
Bitcoin URIs do not support scientific notation, and I don't know why Coinbase expected that to work. Bitcoin-Qt (rightly) gives an error when trying to parse this URI.
They probably didn't do it on purpose, it's likely the default in android to switch to scientific notation at some number of decimals.