X protocol errors using lxde on top of Xdmx

I'm trying to setup Xdmx with lxde. Now I have some issues: lxde itself works fine, but as soon as I use it on top of Xdmx, I keep getting various X protocol errors, even when only connecting to a local display. When xrender is enabled, no fonts are rendered and the command line outputs several times:

(**) dmx: dmxErrorHandler: RenderBadPicture (invalid Picture parameter)  
(**)                       Major opcode: 138 (RENDER)  
(**)                       Minor opcode: 10 (RenderTrapezoids)  
(**)                       ResourceID:   (varies, e.g. 0x140037c)  
(**)                       Failed serial number:  (varies, e.g. 5147)  
(**)                       Current serial number: (varies, e.g. 5170)  

I can prevent that with using -norender as argument, but even when I run

startx -- /usr/bin/Xdmx :1 -display :0 -noglxproxy -norender  

emacs still fails when my mouse hovers over it. It terminates with errors like

X protocol error: BadAlloc (insufficient resources for operations) on protocol request 78  

or

(emacs:1882): Gtk-CRITICAL **: gtk_container_remove: assertion 'gtk_widget_get_parent (widget) == GTK_WIDGET (container) || GTK_IS_ASSISTANT (container) || GTK_IS_ACTION_BAR (container)' failed  
X protocol error: BadDrawable (invalid Pixmap or Window parameter) on protocol request 14

lxterminal also doesn't work:

The program 'lxterminal' received an X Windows System error.  
This probably reflects a bug in the program.
The error was 'BadAlloc (insufficient resource for operation)'.  
  (Details: serial 107 error_code 11 request_code 78 minor_code 0)

Is there anything I can do to resolve this?

(xorg-server 1.16.4)