The Mahabharata, one of the two Itihasas, begins with the tale of the Sarpa Satra of King Janamejaya, during which the epic was narrated to him by Janamejaya. The Sarpa Satra was a 12-year Yajna conducted by Janamejaya to avenge his father Parikshit's death by the Snake Takshaka, by killing all the snakes. Fortunately (?) this act of his was stopped by Sage Astika, the son of Jaratkaru and Manasa Devi. (Here too there is a difference, as in the Bhagavatam, Janamejaya is stopped by Brhaspati.)
Now, the background of this story is the death of Parikshit. In the Adi Parva, it is described that Maharaja Parikshit, while hunting, gets thirsty and reaches the Ashrama of Maharshi Shamika. When Maharshi Shamika doesn't respong to his request for water, due to his meditation, Parikshit gets angry and drapes a dead snake around the Maharshi's neck and leaves. He is noticed by the sage's son Shringi, who pronounces a curse on the King to be killed by the Snake King Takshaka within seven days.
When Parikshit is informed, he becomes paranoid and builds a high tower, inaccessible to all but him, and resides within it with all his supplies. But Takshaka decides to enter one of the fruits to be taken for Parikshit. He stops a rishi named Kashyapa (not the famous Kashyapa) who had been on his way to chant the Mrta Sanjeevani on a dead Parikshit and bring him to life, thereby obtaining lot of rewards. Takshaka gives Kashyapa a lot of wealth and then enters a fruit. When Parikshit bites into the fruit Takshaka comes out and bites him back, killing him. (The Devi Bhagavatam adds that Parikshit attains Moksha when his son listens to Devi Bhagavatam (!) and worships Devi.)
But the Srimad Bhagavatam is unaware of the above story from the tower building part. In Srimad Bhagavatam, as soon as Parikshit knows of his fate, he goes to the banks of the Ganga, where he meets several rishis, led by Shukadeva Gosvami, who imparts to him Srimad Bhagavatam within seven days, following which Parikshit is free from all desires, and in the midst of all the rishis happily accepts death as Takshaka (who has here too stopped Kashyapa) bites him and burns him to ashes.
So, why this huge difference between the two stories? Because the Parishit and Shukadeva story leads to Srimad Bhagavatam, and the other to Devi Bhagavata directly and indirectly to the Mahabharata (since the story of the tower is present in the Mahabharata.)
We can not dismiss this as an interpolation, because there seems to be no cause for interpolation; if anything it only advances the plot.
So, once again, why is there such a glaring difference between the two scriptures?