When parent check-in doesn't have an R-card in manifest, Fossil fails to create a branch from this check-in with error "unable to install new manifest". This is because Fossil creates manifest for a new branch which contains a line: "R " (and no checksum), instead of not adding an R-card at all, and manifest_parse() fails to parse such manifests.

Fix (patch is not against tip, but you get the idea):

<verbatim>
--- src/branch.c
+++ src/branch.c
@@ -99,11 +99,13 @@
     }
     blob_append(&branch, "\n", 1);
   }
   zUuid = db_text(0, "SELECT uuid FROM blob WHERE rid=%d", rootid);
   blob_appendf(&branch, "P %s\n", zUuid);
-  blob_appendf(&branch, "R %s\n", pParent->zRepoCksum);
+  if( pParent->zRepoCksum ){
+    blob_appendf(&branch, "R %s\n", pParent->zRepoCksum);
+  }
   manifest_destroy(pParent);

   /* Add the symbolic branch name and the "branch" tag to identify
   ** this as a new branch */
   if( zColor!=0 ){
</verbatim>