I have this problem too, same config (MacBook Leopard 10.5.8, Spanish ISO keyboard layout (es_ES), Code::Blocks svn build Mar 1, 2010)
I cant write '{' and '[' simbols on source code screen, but I can write them on search form and others fields...
I have not active plugins on my configuration.
If I switch the keyboard configuration to US I can write correctly.
Hope you can help.
Thank you