--- gawk-3.1.5/eval.c.wconcat	2006-02-14 09:40:54.000000000 +0100
+++ gawk-3.1.5/eval.c	2006-02-14 09:43:33.000000000 +0100
@@ -1176,6 +1176,13 @@
 			memcpy(l->stptr + l->stlen, r->stptr, r->stlen);
 			l->stlen += r->stlen;
 			l->stptr[l->stlen] = '\0';
+#if defined MBS_SUPPORT
+			if (r->wstptr != NULL)
+				free(r->wstptr);
+			r->wstptr = NULL;
+			r->wstlen = 0;
+			r->flags &= ~WSTRCUR;
+#endif /* MBS_SUPPORT */
 		} else {
 			char *nval;
 			size_t nlen = l->stlen + r->stlen + 2;