Hello Sanish,
This is because the FD is not really the current lowest distance to the destination - rather, it is a record of the lowest distance to the destination since the last time the route went from Active to Passive state. In other words, the FD is a historical minimum of the distance to the destination, with the history starting again when the route transitions from Active to Passive state. If the current distance increases in such a way that no diffusing computation is required (i.e. after the distance increase, the router providing the least actual distance still passed the feasibility condition check), the FD will remain at its present value while the current distance increases. Exactly this has happened in your case.
The FD, contrary to popular belief, is not the current distance to the destination, and it is not advertised in EIGRP. The FD is assigned to each known route but is used only locally by each router in the Feasibility Condition.
Best regards,
Peter
