Ive been having some software problems but i hope this works.
Highrailer, if you go in & edit your initial post, removing the
tags but leaving the [bigimg][/bigimg] ones as is - as I've done here - that should fix things. Seems like when the two lots of tags are both present at the same time, they fight each other and the desired effect of the big image tags gets negated as a result.
For a guess, I'll say somewhere in the suburbs of Ballarat