While working with workflow, we can map the same data type field while creating or updating a record. But there was an issue with optionset mapping.
I have used workflow quite a lot time but recently I was mapping an option set with another option set which has the same value, but it was not showing the value. I found that due to local option set not allowed to map.
As you can see in the below screen it is not showing the field to map.
To overcome with this, we need to perform the below three steps
1.) Create a global option set
2.) Create local option set using the global option set on source record
3.) Create local option set using the global option set on target record
Once above field is created you will able to see the mapping field
1.) Since we are creating another field, make sure that you have kept the history value of old record.
2.) Do not delete the field while creating new field mapping
Hope this helps you to map optionset using workflow.