[BUG] "git fetch --tags" seems to be broken with recent change on 'master'

I haven't started digging this through, but just a heads-up.

One of the recent changes we made on 'master' (either Shawn's protocol tweak or my progressive common commit discovery) seems to have broken "git fetch --tags" and possibly other forms of fetch, failing with SIGPIPE. From the stack trace I am guessing that the server side might be closing the connection prematurely while the client still wants to say something to it.

#0  0x000000362d80e470 in __write_nocancel () from /lib64/libpthread.so.0
#1  0x00000000005064de in xwrite (fd=9, buf=0x896480, len=804) at wrapper.c:137
#2  0x00000000004c6570 in safe_write (fd=9, buf=0x896480, n=804) at pkt-line.c:68
#3  0x000000000042ada5 in send_request (fd=9, buf=0x7fffffffdd40)
    at builtin/fetch-pack.c:219
#4  0x000000000042b458 in find_common (fd=0x7c6740, 
    result_sha1=0x7fffffffde20 "\200\203}", refs=0x0) at builtin/fetch-pack.c:368
#5  0x000000000042c48c in do_fetch_pack (fd=0x7c6740, orig_ref=0x7d8460, nr_match=1, 
    match=0x7d8380, pack_lockfile=0x7c6700) at builtin/fetch-pack.c:765
#6  0x000000000042cd23 in fetch_pack (my_args=0x7fffffffdfc0, fd=0x7c6740, conn=0x7d83a0, 
    ref=0x7d8460, dest=0x7f86d0 "/pub/scm/git/git.git", nr_heads=1, heads=0x7d8380, 
    pack_lockfile=0x7c6700) at builtin/fetch-pack.c:985
#7  0x00000000004f83d0 in fetch_refs_via_pack (transport=0x7c66a0, nr_heads=1, 
    to_fetch=0x7f8600) at transport.c:542
#8  0x00000000004f9c5c in transport_fetch_refs (transport=0x7c66a0, refs=0x7e5610)
    at transport.c:1112
#9  0x000000000042e3aa in fetch_refs (transport=0x7c66a0, ref_map=0x7e5610)
    at builtin/fetch.c:513
#10 0x000000000042eb97 in do_fetch (transport=0x7c66a0, refs=0x7c6b80, ref_count=0)
    at builtin/fetch.c:712
#11 0x000000000042f431 in fetch_one (remote=0x7c6420, argc=0, argv=0x7fffffffe4e8)
    at builtin/fetch.c:895
#12 0x000000000042f6c6 in cmd_fetch (argc=1, argv=0x7fffffffe4e0, prefix=0x0)
    at builtin/fetch.c:947
#13 0x000000000040484c in run_builtin (p=0x771de8, argc=3, argv=0x7fffffffe4e0)
    at git.c:290
#14 0x00000000004049e8 in handle_internal_command (argc=3, argv=0x7fffffffe4e0)
    at git.c:448
#15 0x0000000000404ae2 in run_argv (argcp=0x7fffffffe3cc, argv=0x7fffffffe3c0) at git.c:492
#16 0x0000000000404c6a in main (argc=3, argv=0x7fffffffe4e0) at git.c:565