When tracing, traces are auto-merged if the trace names are the same and they are overlapping. If the user undoes this action with ctrl-z, two traces are left: the original trace and a new non-merged trace. However, undoing should leave the user with only the original trace. (Note: A user really might want overlapping traces with the same name that are not merged, but this can be achieved already by turning off auto-merging.)
When tracing, traces are auto-merged if the trace names are the same and they are overlapping. If the user undoes this action with ctrl-z, two traces are left: the original trace and a new non-merged trace. However, undoing should leave the user with only the original trace. (Note: A user really might want overlapping traces with the same name that are not merged, but this can be achieved already by turning off auto-merging.)