I use thg version 126.96.36.199+20-395c8e21d348 on Windows 7.
In the commit dialog I open the shelve tool with the icon above the diff window ("Open shelve tool"). In the shelve too I double-click a file, which opens the Hg file log viewer. The newly opened log viewer window jumps to the back and cannot be brought to the front. Clicking on the window just results in an audible alert.
After closing the shelve tool window, the log viewer window can be brought to the front by clicking on it.