Unless I'm derping on my bb:

[i] italic [/i]

non-italic
[i] italic [/i]

[b]bold [/b]
non-bold

[b] bold [/b]

[centre]test [/centre]
test
[centre] test [/centre]

[quote] test [/quote]
test
[quote]test[/quote]

Multiple's don't work properly.

Except Quote.