Hi Member,
Not really a solution just some hacky but maybe acceptable workarrounds can be found here
c# - Removing the default MDI menu of a MDI Container form when a MDI Child is maximized - Stack Overflow[
^]
But you maybe allready have seen this "Solutions"...
I just wanted to share my experience with applications like yours (borderless forms with custom/simulated system menu):
After Messing arround with MDIContainer and Forms I decided to implement my own logic - It's not that difficult if you just want to "simulate" normal window behavior - think about it - just some simple positioning logic. The Sub-forms where UserControls just layered on top of each other (in normal Z-Order) on the main-form. And I left all the hassles with MDI behind me...
Kind regards
Johannes