Same issue here:

This is xfdesktop version 4.10.0, running on Xfce 4.10.
Built with GTK+ 2.24.10, linked with GTK+ 2.24.10.
Build options:
    Desktop Menu:        enabled
    Desktop Icons:       enabled
    Desktop File Icons:  enabled

I have a single monitor with a resolution of 1920x1080. Since installation I have noticed that often when I log in the icons move. Now I have seen that /home/fred/.config/xfce4/desktop contains multiple icons.screen files with varying resolutions (I've not included all of them here):

-rw-rw---- 1 fred fred 1722 Aug 20 08:57 icons.screen0-1904x997.rc
-rw-rw---- 1 fred fred 1722 Aug 21 12:57 icons.screen0-1904x998.rc
-rw-rw---- 1 fred fred 2178 Jul  3 14:09 icons.screen0-1920x1080.rc

As you can see there is one that was created today with a timestamp of when I logged in (and the icons moved). The other one on August the 20th was the login on that day when again my icons moved.

I think something during login is determining the wrong screen size and ignoring the resolution (in Display the resolution tells me it's 1920x1080). It's creating a new icons.screen file that then causes the icons on the desktop to move.

My desktop is quite busy and I have icons in specific places for specific types of admin jobs. When the icons move it takes a bit of time to sort them knowing that sooner or later it will do it again....

gymka,
  Can you post the output of xfdesktop --version? Does this happen for you during login? Or as you add/remove external montiors? Or both?

This is xfdesktop version 4.10.0, running on Xfce 4.10.
Built with GTK+ 2.24.10, linked with GTK+ 2.24.10.
Build options:
    Desktop Menu:        enabled
    Desktop Icons:       enabled
    Desktop File Icons:  enabled

it's caused by external monitor. my monitor resolution 1280x1024 and TV resolution 800x600, so sometimes after disabling/enabling TV my icons arranged by 800x600 resolution and not by 1280x1024

In Xfce 4.10, xfdesktop should do a better job of keeping track of your icon placement.

i'm using GIT version of thunar(and whole xfce) and still has same problems as thread author:)

I have XFCE 4.8 and Thunar 1.2.1 and after arranging my desktop icons in concrete positions of the "invisible desktop grid", I find that the icons are messed up after re-login, or after switching to the external monitor, etc.

I ended putting all my icons in the left-up side of the desktop, so that they were not affected with the resolution changes (at least, those that were in the right side of the desktop) and they are messed in any case.

With nautilus, icons "remember" their position and this does not happen. Can Thunar do this?

Thanks.