Hello,
it is very simple to reproduce it. Currently tested on version 8.53
Just create a new form application, put SkinManager and SkinProvider there, add and set “Mint” as internal skin, enable extended borders. Run it.
Open properties of this application in Sysinternal's Process Explorer. Check count of GDI handles in performance tab.
Just minimize the main form (form1) and restore it again from taskbar. Count of GDI handles is increased. Minimize – restore again, and count of GDI handles is higher again.
Mint skin + ext borders = GDI handles leak
Mint and no ext borders = OK
Beijing Ext + ext borders = OK
Beijing Ext and no ext borders = OK
I did not test all skins, but currently I only know that this problem occurs with Mint skin and ext borders enabled.