1. the pointer sp points to p: sp = p;
2. stupid_insert inserts at p which may cause a reallocation of text
3. p is adjusted to the reallocated text
4. sp still points to the old location which is most likely invalid
5. sp is used in: strchr(")]}", *sp), showmatching(sp)

// line 1838
#if ENABLE_FEATURE_VI_SETOPTS
		// insert a char into text[]
		char *sp;		// "save p"
#endif

		if (c == 13)
			c = '\n';	// translate \r to \n
#if ENABLE_FEATURE_VI_SETOPTS
		sp = p;			// remember addr of insert
#endif
		p += 1 + stupid_insert(p, c);	// insert the char
#if ENABLE_FEATURE_VI_SETOPTS
		if (showmatch && strchr(")]}", *sp) != NULL) {
			showmatching(sp);
		}