I've been with GloBill for three plus years and only had one recent check bounce when they did the account switch. They repaid me the amount plus the NSF fees just recently. All the checks since then have been deposited without any problems.
I wouldn't sweat it. They're a great company and will make good on whatever you are out. They did say that in a number of cases they are in fact investigating because some webmasters are of course trying to take advantage of the glitch and are inflating their NSF fees or even falsely claiming bouncies where there were no bouncies.