> From what I understand this is because the
> compressed flag is set to 0 after compression in
> htsback.c, and it seems like the diff below fixes
> the problem:

Thanks - patch applied! (slightly modified)

===================================================================
--- htsback.c   (revision 121)
+++ htsback.c   (working copy)
@@ -560,7 +560,6 @@
                                                // unflag
                                        }
                                }
-                               back[p].r.compressed=0;
 #endif

                                /* Write mode to disk */
@@ -664,6 +663,11 @@
                                       
fprintf(cache->txt,LLintP,(LLint)back[p].r.totalsize);
                                        fprintf(cache->txt,"\t%s\t",flags);
                                }
+
+#if HTS_USEZLIB
+                               back[p].r.compressed=0;
+#endif
+
                                if (back[p].r.statuscode == HTTP_OK) {
                                        if (back[p].r.size>=0) {
                                                if
(strcmp(back[p].url_fil,"/robots.txt") !=0 ) {