We at OW were told about the username change when Whaling came out, because it was using the "new" database setup. I know, because converting "Janet Jaguar" to "JanetJaguar" was so fraught with problems, Chris S. had to manually reset my whole account. He let me keep the space on the forum. But if you look at my posts, like the FAQ, on the Whaling Talk site you will see the space has been removed. It didn't bother me much, I just saw it as being the guinea pig who protected the devs from 10,000 such problems when they went global.
I think - I don't know - that every single person from OW with a space or symbols ran into so much trouble, they spent time squashing the bugs before extending it to the million plus volunteers in the Zoo database. For sure, underlines were not used as a space replacer back then. The major mistake this time was failing to announce it first.