[CRASH] in GC, in compact_string_chars()

I see a corruption in a string_char_block struture. I remember that I have already been debugging this place: if (FREE_STRUCT_P (from_s_chars)) { fullsize = ((struct unused_string_chars *) from_s_chars)->fullsize; from_pos += fullsize; continue; } string = from_s_chars->string; assert (!(FREE_STRUCT_P (string))); In the above assert statement, string variable has an ascii value, like 0x4C282020 (this is from modeline: " (L" isp interaction), or something else, but always characters. This no doubt ends up with GPF, or SEGV, whatever you call this sweetie on your system. I spent my whole life and borrowed another one catching the reason for that, and all to no avail. Does anybody remember something related to such a crash? I have no reproduction. This is the third time in the last 2 days I'm getting this, and the first time in debug build. Kirill, clueless. Backtrace, of no value, just in case: compact_string_chars() line 4049 + 3 bytes gc_sweep() line 4254 garbage_collect_1() line 4559 funcall_recording_as(int 555206584, int 3, int * 0x0082e460) line 3116 Ffuncall(int 3, int * 0x0082e460) line 3238 + 19 bytes call2(int 555206584, int 1104342316, int -1581761356) line 3928 + 11 bytes map_keymap_mapper(const key_data * 0x0082e49c, int -1581761356, void * 0x2117c7b8) line 2971 + 28 bytes map_keymap_unsorted_mapper(void * 0xc0000077, void * 0xa1b83cb4, void * 0x0082e5a8) line 2808 + 20 bytes maphash(int (void *, void *, void *)* 0x0109dd63 map_keymap_unsorted_mapper(void *, void *, void *), _C_hashtable * 0x0082e4ec, void * 0x0082e5a8) line 470 + 20 bytes elisp_maphash(int (void *, void *, void *)* 0x0109dd63 map_keymap_unsorted_mapper(void *, void *, void *), int 565628096, void * 0x0082e5a8) line 886 + 17 bytes map_keymap_unsorted_mapper(void * 0x00000001, void * 0x21b6cf80, void * 0x0082e5a8) line 2800 + 30 bytes maphash(int (void *, void *, void *)* 0x0109dd63 map_keymap_unsorted_mapper(void *, void *, void *), _C_hashtable * 0x0082e574, void * 0x0082e5a8) line 470 + 20 bytes elisp_maphash(int (void *, void *, void *)* 0x0109dd63 map_keymap_unsorted_mapper(void *, void *, void *), int 565625536, void * 0x0082e5a8) line 886 + 17 bytes map_keymap(int 565625536, int 0, void (const key_data *, int, void *)* 0x0109dce6 map_keymap_mapper(const key_data *, int, void *), void * 0x2117c7b8) line 2992 + 18 bytes Fmap_keymap(int 555206584, int 565625216, int -1582282748) line 3030 + 45 bytes funcall_recording_as(int -1582147484, int 2, int * 0x0082e744) line 3193 + 105 bytes Ffuncall(int 3, int * 0x0082e744) line 3238 + 19 bytes Fbyte_code(int 1628948484, int -2129147840, int 4) line 416 + 16 bytes funcall_lambda(int 555206764, int 4, int * 0x0082ea28) line 3599 + 35 bytes funcall_recording_as(int -1581824388, int 4, int * 0x0082ea24) line 3200 + 20 bytes Ffuncall(int 5, int * 0x0082ea24) line 3238 + 19 bytes Fbyte_code(int 1628948004, int -2129148316, int 5) line 416 + 16 bytes funcall_lambda(int 555206312, int 1, int * 0x0082f2b4) line 3599 + 35 bytes funcall_recording_as(int -1582147852, int 1, int * 0x0082f2b0) line 3200 + 20 bytes Ffuncall(int 2, int * 0x0082f2b0) line 3238 + 19 bytes Fbyte_code(int 1641182160, int -2117236224, int 4) line 416 + 16 bytes Feval(int 1104011172) line 3063 + 153 bytes readevalloop(int 565436672, int 1639592672, int (int)* 0x0104a0f2 Feval(int), int 0) line 1340 + 7 bytes Fload_internal(int 1639592672, int -1582282748, int -1582282748, int -1582282748, int -1582152140, int -1582282748) line 747 + 23 bytes funcall_recording_as(int -1582145900, int 5, int * 0x0082f958) line 3193 + 207 bytes Ffuncall(int 6, int * 0x0082f958) line 3238 + 19 bytes Fbyte_code(int 1629338824, int -2128757412, int 11) line 416 + 16 bytes funcall_lambda(int 555597388, int 4, int * 0x0082fb98) line 3599 + 35 bytes funcall_recording_as(int -1582145708, int 4, int * 0x0082fb94) line 3200 + 20 bytes Ffuncall(int 5, int * 0x0082fb94) line 3238 + 19 bytes call4(int -1582145708, int 1639592672, int -1582282748, int -1582282748, int -1582282748) line 3964 + 11 bytes do_autoload(int 1103146012, int -1581690780) line 2761 + 80 bytes Fcommand_execute(int -1581690780, int -1582282748, int -1582282748) line 2566 + 13 bytes execute_command_event(command_builder * 0x01c37640, int 565448908) line 4289 + 25 bytes Fdispatch_event(int 565448908) line 4591 + 71 bytes Fcommand_loop_1() line 574 + 9 bytes command_loop_1(int -1582282748) line 495 condition_case_1(int -1582282652, int (int)* 0x0102ee06 command_loop_1(int), int -1582282748, int (int, int)* 0x0102e8b4 cmd_error(int, int), int -1582282748) line 1653 + 7 bytes command_loop_3() line 256 + 35 bytes command_loop_2(int -1582282748) line 268 internal_catch(int -1582172356, int (int)* 0x0102ea04 command_loop_2(int), int -1582282748, int * 0x00000000) line 1328 + 7 bytes initial_command_loop(int -1582282748) line 305 + 26 bytes STACK_TRACE_EYE_CATCHER(int 1, char * * 0x01b2e340, char * * 0x01b84d00, int 0) line 1677 + 9 bytes main(int 1, char * * 0x01b2e340, char * * 0x01b84d00) line 2094 + 21 bytes mainCRTStartup + 211 bytes _start() line 118 KERNEL32! 77f1b304()