custom task started from workflow

I know how to create a custom task add-in using the API, and I know how to get a task to execute during a workflow transition, but I'm having trouble getting my custom task add-in to run.  My task shows in the add-ins and task lists, I can run my task from a menu command, but I can't get my custom task to show up in the "Select task to execute:" drop down list within the workflow transition action.  I assumed it would be available in this drop down automatically when the task was created.  I even tried adding a hook (oCmdMgr.AddHook(EdmCmdType.EdmCmd_PreState)) without any luck.  What am I missing or is this not possible?