21.0b46 native crash

I have reported a crash with 21.0b46 native under NT. In fact, this happens constantly when using Gnus. The crash happens in gc, sometimes very quickly, and it seems that some : struct string_chars { struct Lisp_String *string; unsigned char chars[1]; }; is overwritten with data : - from_s_chars 0x021d95b8 + string 0x70756f72 + chars 0x021d95bc "* {nntp:news.ese-metz.fr} (Group PenDel PC)----Top------------------------------------ " The string member is invalid, and has always the same value. This seems to me like ascii chars : 70756F72 = l q k n but I may be wrong. It happens even when compiled without any optimisation, without any strange options (like USE_UNION_TYPE, USE_MINIMAL_TAGBITS, USE_INDEXED_LRECORD_IMPLEMENTATION) Anybody has an idea ? Fabrice