On the subject of ba, ib, and ka

[Fubbles the Baby Cow]

The Osirian culture believes that a person's essence is divided into three parts:

The ba: The personality, or psyche
The ib: The emotions, will, and thoughts
The ka: The "vital spark"

If all three pieces are intact at the time of a person's death, they are ready for the journey to the afterlife.

This brings me to a question regarding the main plot of Mummy's Mask:

Spoiler:

When Pharaoh Hakotep died, his ib and ka were stolen. The ib was trapped in an artifact called The heart of Hakotep, and hidden in Sothis. His ka was similarly trapped in an artifact named The mask of the Forgotten Pharaoh, and hidden in Wati. Hakotep's ba remained undisturbed and left within his dead body.

When the priestess Serethet stumbles upon The heart of Hakotep, she is possessed by Hakotep and now housed two intellects within her mind: Her own and Hakotep's. When Nebta-Khufre locates The mask of the Forgotten Pharaoh, he gets to be a super-necromancer, thanks to the powers of the mask.

Here's the crux of the biscuit: When Netba-Khufre is defeated by the PCs, Hakotep's ka returns to the Mask of the Forgotten Pharaoh, and the PC that wears the mask gains some of its abilities. However, when Serethet is defeated, Hakotep's ib returns to Hakotep, and he awakens as a mummy. Why does the ka return to its prison when the ib is free to return to its owner? Shouldn't the elements of the soul all behave the same way? Both return to the owner, or both return to their prisons? Either way, the AP is significantly changed if both behave the same, but I'm looking for some reasoning why the ka and ib behave differently.

[Warped Savant]

Hidden behind a spoiler tag as the title of the thread doesn't warn of spoilers:

Spoiler:

There's no heart for his ib to return to.
It was eaten.