Several GTK-2 applications (medit, Geany-GTK-2, GIMP) often crash on large text
selection or copy operations. But only if a clipboard manager (e.g. KDE
klipper) is running.

PLEASE tell me, if you need more information. I'll happily provide them!

I didn't test the GIMP issues, but they match the description pretty well:
https://gitlab.gnome.org/GNOME/gimp/issues/789
https://gitlab.gnome.org/GNOME/gimp/issues/2733
https://github.com/hluk/CopyQ/issues/636


Tested medit and Geany on a ~550 KB textfile, containing about 3900 lines.
Selecting from the last line upward to the first line.

line="$(for i in {0..128}; do echo -n a; done)"; for i in {0..3900}; do echo
"${line}"; done > testfile.txt

medit (openSUSE-15.1 OSS repo)
The program 'medit' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadWindow (invalid Window parameter)'.
  (Details: serial 3588 error_code 3 request_code 18 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
# gdb
Thread 1 "medit" hit Breakpoint 1, gdk_x_error (display=0x555555a91cd0,
error=0x7fffffffd3f0) at gdkmain-x11.c:458
458     {
(gdb) bt
#0  0x00007ffff6676190 in gdk_x_error (display=0x555555a91cd0,
error=0x7fffffffd3f0) at gdkmain-x11.c:458
#1  0x00007ffff76d84aa in _XError (dpy=dpy@entry=0x555555a91cd0,
rep=rep@entry=0x5555564a4850) at XlibInt.c:1434
#2  0x00007ffff76d53db in handle_error (dpy=0x555555a91cd0, err=0x5555564a4850,
in_XReply=<optimized out>) at xcb_io.c:199
#3  0x00007ffff76d5485 in handle_response (dpy=0x555555a91cd0,
response=0x5555564a4850, in_XReply=<optimized out>) at xcb_io.c:311
#4  0x00007ffff76d63e0 in _XReply (dpy=dpy@entry=0x555555a91cd0,
rep=rep@entry=0x7fffffffd5a0, extra=extra@entry=0, discard=discard@entry=1) at
xcb_io.c:621
#5  0x00007ffff76d1d7d in XSync (dpy=0x555555a91cd0, discard=discard@entry=0)
at Sync.c:44
#6  0x00007ffff76d1e1b in _XSyncFunction (dpy=<optimized out>) at Synchro.c:35
#7  0x00007ffff76b2293 in XChangeProperty
    (dpy=0x555555a91cd0, w=w@entry=44040439, property=property@entry=329,
type=type@entry=389, format=format@entry=8, mode=mode@entry=0,
data=0x55555657ddd0 "2019-07-19T12:58:49.786749+02:00 DE08Provaia02
systemd-modules-load[1135]: Inserted module
'sg'\n2019-07-19T12:58:49.786782+02:00 DE08Provaia02 systemd-sysusers[1157]:
Creating group adm with gid 491.\n"..., nelements=262144) at ChProp.c:92
#8  0x00007ffff6678630 in IA__gdk_property_change
    (window=0x5555564ae900 [GdkWindow], property=0x89, type=0x47, format=8,
mode=mode@entry=GDK_PROP_MODE_REPLACE, data=0x55555657ddd0
"2019-07-19T12:58:49.786749+02:00 DE08Provaia02 systemd-modules-load[1135]:
Inserted module 'sg'\n2019-07-19T12:58:49.786782+02:00 DE08Provaia02
systemd-sysusers[1157]: Creating group adm with gid 491.\n"...,
nelements=262144) at gdkproperty-x11.c:732
#9  0x00007ffff6a6089f in _gtk_selection_incr_event (window=<optimized out>,
event=event@entry=0x555556474800) at gtkselection.c:2593
#10 0x00007ffff69fd0f4 in IA__gtk_main_do_event (event=0x555556474800) at
gtkmain.c:1540
#11 0x00007ffff666f08c in gdk_event_dispatch (source=<optimized out>,
callback=<optimized out>, user_data=<optimized out>) at gdkevents-x11.c:2425
#12 0x00007ffff5178e87 in g_main_dispatch (context=0x555555a78600) at
gmain.c:3142
#13 0x00007ffff5178e87 in g_main_context_dispatch
(context=context@entry=0x555555a78600) at gmain.c:3795
#14 0x00007ffff5179230 in g_main_context_iterate (context=0x555555a78600,
block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at
gmain.c:3868
#15 0x00007ffff5179542 in g_main_loop_run (loop=0x555555a49880) at gmain.c:4064
#16 0x00007ffff69fc097 in IA__gtk_main () at gtkmain.c:1270
#17 0x00005555556cda83 in moo_app_run (app=0x555555b14260 [MeditApp]) at
mooapp/mooapp.c:908
#18 0x00005555555b8243 in medit_main (argv=<optimized out>, argc=<optimized
out>) at medit-app/main.c:843
#19 0x00005555555b8243 in main (argc=<optimized out>, argv=<optimized out>) at
medit-app/main.c:854

geany-1.35 compiled with "--enable-gtk2 --disable-gtk3"
The program 'geany' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadWindow (invalid Window parameter)'.
  (Details: serial 7406 error_code 3 request_code 18 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
Geany issue: https://github.com/geany/geany/issues/1042