Maybe you already know, but I didn't found a bug for this, so I submit one ...

The following columns cannot be exported in CSV:
category_id, due_date, description, steps_to_reproduce, additional_information, attachment_count, bugnotes_count, edit, overdue

Doing so, I get an error in the resulting CSV file (please see attachment).

I got the names for possible columns from 1.2.0RC2, where there is an option in the "My Account" page. Maybe the problem is already fixed in that version.

The following options are working:
array (0 => id, 1 => project_id, 2 => reporter_id, 3 => handler_id, 4 => duplicate_id, 5 => priority, 6 => severity, 7 => reproducibility, 8 => status, 9 => resolution, 10 => date_submitted, 11 => last_updated, 12 => os, 13 => os_build, 14 => platform, 15 => version, 16 => fixed_in_version, 17 => target_version, 18 => view_state, 19 => summary, 20 => sponsorship_total, 21 => selection)