This bug is discussed in trac ticket #28617 <https://trac.sagemath.org/ticket/28617> (which recently received a patch).
-- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/90133b60-c51a-47b7-ad5c-f2409f03b1a1o%40googlegroups.com.