This seems to be all in how you made your post.
This is how you posted, and the
improper way to have a line break after your tag:
Code
[B]test
[/B]one
[B]test
[/B]two
Here is the
proper way:
Code
[B]test[/B]
one
[B]test[/B]
two
Notice in the first (improper) example that you hit enter inside the bold bbcode, whereas in the second, it occurs outside the block.