PVS-Studio warning V579 for Source SDK

typedef struct message_s
{
  ....
  char    *text;
  ....
} message_t;

int CMessageCharsPanel::AddText(....)
{
  ....
  msg->text = new char[ Q_strlen( data ) + 1 ];
  Assert( msg->text );
  Q_strncpy( msg->text, data, sizeof( msg->text ) );
  ....
}

This suspicious code was found in Source SDK project by PVS-Studio static code analyzer.
Warning message is:
V579 The V_strncpy function receives the pointer and its size as arguments. It is possibly a mistake. Inspect the third argument. Client (HL2) vgui_messagechars.cpp 240

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