It could be a shifiting border or the difference between the old province borders and the new County Borders. A note on Östervåla in Arkiv Digital:
By 1863 the majority of the parish was in Västmanland County and a small part (Ingeborgsbo) in Uppsala County. 1863-07-22 Ingeborgsbo was transferred to Tierp in Uppsala county. In 1890, Ingeborgsbo was returned to v, now in Västmanland County.