ONLINE v.4 logical logs problems

We're running Informix-Online v.4. The database is about 7 gigs and consists of several hundred tables, many of which are >1m rows and one which is >13m rows. Whenever I try to drop or create an index on a large loaded table the engine completely screws up because it creates a transaction for the process and fills up the logical logs. When they inevitably become full, it doesn't back out of the transaction, like you might think it should, instead it falls over and asks for a backup to be carried out to clear the logical logs. Trouble is, it can't do the backup because the engine has stopped dead. Whenever this has happened I've had to recreate the entire system from backups. It has happened when I've done a query which Informix has thought it can speed up by creating a temporary index. Any of you have experience with this problem? When it next happens, is there anything I can do without having to restore from tapes, which takes about 5 hours? Upgrading is something I'd like to avoid as I've been told that there are worse bugs with the later versions. TIA, Stephen