Whilst fitting the waste to our new bath, I noticed that one of the
joists of the bathroom floor is not supported properly at one end -
the brick it should be sitting on has fallen back into the cavity and
is supporting the joist only with its front edge. Difficult to
describe so I've taken a photo (12KB):

http://www.darboss.com/images/joist.jpg

Just for background, the bathroom is located above our garage, so
access to the underside of the bathroom floor is easy. The joists span
the width of the garage.

Question is, since this joist is directly under where we are
positioning the new bath, and its a big corner bath, so potentially
quite heavy, should I repair this?

If I need to repair it, what would be the best way? I've already had
two suggestions:

1. Support the joist, and refit brick.

2. Don't move anything and add mortar to support the out of place
brick.

I can't really understand why the brick is like that in the first
place (it is right next to the soil stack, which sits in the cavity
and breaks the inside garage wall), and why there appears to be no
evidence of mortar ever being used on it.

Any suggestions/advice would be greatly appreciated,

Thanks

Sam.