Application exit event raising while invocking functions from other solution

Question

In my c# application used 5 projects which are placed in 2 solutions.

Solution1 : Project 1 - Print module. (class Lib project)
Solution2 : Project 2 - Inventory module. (Application project)

The problem :- Inventory module "Application Exit" event raising after the print function. The print function placed in "Solution1 : Project 1 - Print module". But there is no problem for printing. I wonder why the exit event raising while accessing other solution? Hartley welcomes your detail explanations.