Which window manager?

I'm sorry, somehow I missed to post the bug description.

I'm using LXDE with openbox and have it configured to always put
windows/dialogs onto the monitor where the mouse pointer currently is.
Gimp instead *always* opens the save-file dialog and some other dialogs
on the other monitor. This is confusing behavior and in my case pretty
annoying, since I have pen input on one monitor and have to switch to
the mouse to drag over the window everytime this happens.
I think this might a Gimp bug, because the WM setting works for every
other application I use, except for Gimp.

Deleting ~/.gimp-2.8/sessionrc fixed the problem for me.

There seems to be a bug that caused the file not to get updated. This
caused the dialog windows to show up on the last saved location which
was on another monitor.
I can't investigate this problem anymore, because I deleted the file
without any backup.

Here is something I found digging into the code. It turned out not to be
the cause of the bug, but it's something which just makes you furious
when it takes you hours to debug an issue like that.
But hey, it's not a bug, it's a "feature" ^^ (from gimpsessioninfo.c):

  /*  Window managers and windowing systems suck. They have their own
   *  ideas about WM standards and when it's appropriate to honor
   *  user/application-set window positions and when not. Therefore,
   *  use brute force and "manually" position dialogs whenever they
   *  are shown. This is important especially for transient dialog,
   *  because window managers behave even "smarter" then...
   */

I wonder why gimp has to force window positions at all. The Window
Manager I'm using would have chosen perfectly reasonable places for the
dialog windows (well, I especially configured it to do that).