Removing one character:

Breakpoint 3, text_read_only (propval=58721329) at /Users/magnus/src/emacs/src/textprop.c:89
89        Fsignal (Qtext_read_only, STRINGP (propval) ? Fcons (propval, Qnil) : Qnil);
(gdb) bt
#0  text_read_only (propval=58721329) at /Users/magnus/src/emacs/src/textprop.c:89
#1  0x000a3ee8 in prepare_to_modify_buffer (start=2663756, end=18, preserve_ptr=0x38395b8) at /Users/magnus/src/emacs/src/insdel.c:2036
#2  0x000a3ee8 in prepare_to_modify_buffer (start=2663756, end=18, preserve_ptr=0x38395b8) at /Users/magnus/src/emacs/src/insdel.c:2036
#3  0x000a36f4 in del_range_1 (from=18, to=2684688, prepare=1, ret_string=18) at /Users/magnus/src/emacs/src/insdel.c:1794
#4  0x000b6494 in Fdelete_char (n=0, killflag=2684688) at /Users/magnus/src/emacs/src/cmds.c:256
#5  0x000b6790 in Fdelete_backward_char (n=58721329, killflag=2663756) at /Users/magnus/src/emacs/src/cmds.c:313
#6  0x000e9268 in Ffuncall (nargs=58721329, args=0x38395b8) at /Users/magnus/src/emacs/src/eval.c:2760
#7  0x00115b9c in Fbyte_code (bytestr=58721281, vector=19, maxdepth=58955192) at /Users/magnus/src/emacs/src/bytecode.c:686
#8  0x000e988c in funcall_lambda (fun=58955192, nargs=58721281, arg_vector=0x287b10) at /Users/magnus/src/emacs/src/eval.c:2944
#9  0x000e93b8 in Ffuncall (nargs=58721329, args=0x38395b8) at /Users/magnus/src/emacs/src/eval.c:2814
#10 0x000e4f34 in Fcall_interactively (function=18, record_flag=1, keys=2678648) at /Users/magnus/src/emacs/src/callint.c:877
#11 0x0008c1ec in Fcommand_execute (cmd=58798977, record_flag=2663756, keys=2654832, special=2687268) at /Users/magnus/src/emacs/src/keyboard.c:9679
#12 0x00080e54 in command_loop_1 () at /Users/magnus/src/emacs/src/keyboard.c:1779
#13 0x000e70f8 in internal_condition_case (bfun=0x7fd44 <command_loop_1>, handlers=58766401, hfun=0x7f6d4 <cmd_error>) at /Users/magnus/src/emacs/src/eval.c:1367
#14 0x0007fafc in command_loop_2 () at /Users/magnus/src/emacs/src/keyboard.c:1309
#15 0x000e6b6c in internal_catch (tag=58721329, func=0x7fabc <command_loop_2>, arg=58721281) at /Users/magnus/src/emacs/src/eval.c:1128
#16 0x0007fa54 in command_loop () at /Users/magnus/src/emacs/src/keyboard.c:1288
#17 0x0007f43c in recursive_edit_1 () at /Users/magnus/src/emacs/src/keyboard.c:981
#18 0x0007f5d4 in Frecursive_edit () at /Users/magnus/src/emacs/src/keyboard.c:1042
#19 0x0007e0d4 in main (argc=2684688, argv=0x12) at /Users/magnus/src/emacs/src/emacs.c:1736