I would very much like to, but I don't see a pattern in this, except for that it happened after I closed a connection and another one got into focus.
It looks random. I only saw this twice.

Thanks for the report. Are you able to reproduce this?

I got this just after I closed one of 4 open connections (with CTRL+W). The connection closed and the message window popped up right after that.
All of the connections are with SFTP. Windows 7, 64bit, WinSCP 5.7.5. Using GUI in Commander style.


Stack trace:
(00327554) System::Classes::TStringList::Get
(00327554) System::Classes::TStringList::Get
(00007F5A) TCustomScpExplorerForm::DirViewHistoryChange
(000055A0) TCustomScpExplorerForm::SetTerminal
(00079271) TTerminalManager::TerminalReady
(0007672E) TTerminalManager::SetActiveTerminal
(00019E48) TCustomScpExplorerForm::SessionsPageControlChange
(0021C2F9) Vcl::Controls::TWinControl::WndProc
(002173F0) Vcl::Controls::TControl::Perform
(0021C45F) Vcl::Controls::_17076
(0021C2F9) Vcl::Controls::TWinControl::WndProc
(001D709C) Vcl::Forms::TCustomForm::WndProc
(0078C87D) Vclcommon::C2516_0
(0021B940) Vcl::Controls::TWinControl::MainWndProc
(0034021C) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(00015DE3) USER32.dll
(00015E41) USER32.dll
(0000F107) ntdll.dll.KiUserCallbackDispatcher
(000186C0) USER32.dll.SendMessageW
(0002B06D) COMCTL32.DLL
(00022657) COMCTL32.DLL
(000474F2) COMCTL32.DLL
(000477EC) COMCTL32.DLL
(00047196) COMCTL32.DLL
(000152F7) USER32.dll
(00015D35) USER32.dll
(0001FD22) USER32.dll
(0001FD48) USER32.dll.CallWindowProcW
(0021C40A) Vcl::Controls::TWinControl::DefaultHandler
(0021C2F9) Vcl::Controls::TWinControl::WndProc
(0021B940) Vcl::Controls::TWinControl::MainWndProc
(0034021C) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(0001FD22) USER32.dll
(0001FD48) USER32.dll.CallWindowProcW
(003FEE43) Dragdrop::TDragDrop::WndMethod
(0034021C) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(000167BF) USER32.dll
(00016885) USER32.dll.DispatchMessageW