Background work item error ( work item xxxxx locked by user xxxxx ) enqueue error

Hi,

I have come across with an error in one of the workflow background step.Please refer below and guide me to proceed further.

I have a user decision step in a workflow and in approve branch of the step has a background task which copy the attachments of parked document.Here issue is when the user approves at user decision step ,and processing moves further to approve branch of the step which has a background step which is supposed to be executed by workflow system ( WF-BATCH )  goes to error due to the  work item locked by Dialog user who approved the user decision.  However,this error-ed work item is cleared when the  background job SWWERRE is executed but this delays the posting process for sometime.

Why the background work item is locked  with dialog user who completed the preceding step of a workflow ? Is there any way to avoid this situation to accelerate the document processing ?

Thanks in advance.