if you do /join 0 you will part all channels...

So it has nothing to do with channel locks either seeing how "0" is not a valid channel name. Also, seeing how comma's cant be used in a channel name either doesnt help. the only reason you part all channels on /join #100,000 is because to the server you are joining channel #100 and then after the comma it sees 000 which is 0, so it thinks it wants you to part all channels, so that is what it does.

We don't just write the scripts, we put them to the test! (ScriptBusters)