Error on custom workflow activity when dup detection fails

I have a custom workflow activity that is iterating through a list to create a number of records.  Sometimes, one or more of those records might be duplicates, in which case we don't want them to be created, but we want everything to continue on normally.

I've put the create (telling it to use dup detection) in its own try/catch block, and logging an exception when it happens.

However - if I run this workflow real-time (which is the desired behaviour), it gives an error - the popup just says error and refers me to the log, nothing more.  The log has a bunch of stuff about there being a duplicate, which of course is expected, but I just want it to continue on afterwards as if nothing happened.

The workflow works if:

• It's not creating duplicates
• OR I have dup detection off
• OR I convert it to a background workflow

How can I get it to just create the new ones, log the duplicate ones, and not pop up any error messages to the user?