Here's an underlying bit of the tax code, emphasis mine:   ref

61 Pa. Code § 401.12 - Losses

Losses incurred in the operation of a business may only be used to offset gains from the operation of a business in the year during which the loss was incurred. Losses incurred in the operation of rental property may only be used to offset gains from the operation of rental property in the year during which the loss was incurred. Capital losses, whether long or short term, may only be used to offset capital gains for the year during which the loss was incurred.