It seems that IsWorkstationLocked function (src\mir_core\winver.cpp) wasn't updated a while ago because it reports lock when UAC confirmations pop up. As a consequence, it causes false lock detects e.g. in AdvancedAutoAway plugin which changes status on every UAC confirmation.
AFAIK Windows switches to safe desktop when UAC confirmation pops up, so it causes false detect with current (https://github.com/miranda-ng/miranda-ng/blob/f7bf9527ede3193cfdfd9e30a7a0f20e9a2bf604/src/mir_core/winver.cpp) IsWorkstationLocked implementation:
IsWorkstationLocked
MIR_CORE_DLL(BOOL) IsWorkstationLocked(void)
{
HDESK hDesk = OpenInputDesktop(0, FALSE, DESKTOP_SWITCHDESKTOP);
if (hDesk == NULL)
return true;
TCHAR tszName[100];
DWORD cbName;
BOOL bLocked = (!GetUserObjectInformation(hDesk, UOI_NAME, tszName, SIZEOF(tszName), &cbName) || lstrcmpi(tszName,_T("default")) != 0);
CloseDesktop(hDesk);
return bLocked;
}