Why does the final component have fatḥah in «رَأَيْتُ بَعْلَبَكَّ»?

Al-Murakkabāt — Compound Numerals, the Twelve Exception and Declining Baalbek

• It is genitive with fatḥah
• It is an imperative
• It marks the accusative direct object
• It is genitive because of iḍāfah