geom_label problems when MS-DOS FS label is blank (all spaces)

In this situation libdisk can't parse kern.geom.conftxt and 
sysinstall exits with BARF 171 message.

dmesg:
FreeBSD 7.0-CURRENT #1: Wed May  9 12:18:26 MSD 2007
     chibis_at_free.home.local:/usr/obj/usr/src/sys/GENERIC
[...]
GEOM_LABEL[2]: Tasting ad0s1.
GEOM_LABEL[1]: MSDOSFS: ad0s1: FAT12/FAT16 volume detected.
GEOM_LABEL[0]: Label for provider ad0s1 is msdosfs/ .
GEOM_LABEL[2]: Tasting msdosfs/ .

kern.geom.conftxt:
0 MD md0 67108864 512 u 0 s 512 f 0 fs 0 l 67108864 t swap
0 DISK cd0 0 2048 hd 0 sc 0
0 DISK ad2 20576747520 512 hd 16 sc 63
1 MBR ad2s2 10245795840 512 i 1 o 10330951680 ty 7
1 MBR ad2s1 10330919424 512 i 0 o 32256 ty 165
2 BSD ad2s1f 9642004992 512 i 5 o 688914432 ty 7
2 BSD ad2s1e 209715200 512 i 4 o 479199232 ty 7
2 BSD ad2s1c 10330919424 512 i 2 o 0 ty 0
2 BSD ad2s1b 268435456 512 i 1 o 210763776 ty 1
2 BSD ad2s1a 210763776 512 i 0 o 0 ty 7
0 DISK ad0 3500007424 512 hd 16 sc 63
1 MBR ad0s2 2617638912 512 i 1 o 879427584 ty 165
2 LABEL ufs/objdir 2617638912 512 i 0 o 0
1 MBR ad0s1 879395328 512 i 0 o 32256 ty 6
2 LABEL msdosfs/  879395328 512 i 0 o 0

boot sector dump:
00000000  eb 3c 90 4d 53 44 4f 53  35 2e 30 00 02 20 01 00  |.<.MSDOS5.0.. ..|
00000010  02 c0 03 00 00 f8 d2 00  3f 00 80 00 3f 00 00 00  |........?...?...|
00000020  41 35 1a 00 80 00 29 ac  91 ae 24 20 20 20 20 20  |A5....)...$     |
00000030  20 20 20 20 20 20 46 41  54 31 36 20 20 20 33 c9  |      FAT16   3.|
00000040  8e d1 bc f0 7b 8e d9 b8  00 20 8e c0 fc bd 00 7c  |....{.... .....||
00000050  38 4e 24 7d 24 8b c1 99  e8 3c 01 72 1c 83 eb 3a  |8N$}$....<.r...:|
00000060  66 a1 1c 7c 26 66 3b 07  26 8a 57 fc 75 06 80 ca  |f..|&f;.&.W.u...|
00000070  02 88 56 02 80 c3 10 73  eb 33 c9 8a 46 10 98 f7  |..V....s.3..F...|
00000080  66 16 03 46 1c 13 56 1e  03 46 0e 13 d1 8b 76 11  |f..F..V..F....v.|
00000090  60 89 46 fc 89 56 fe b8  20 00 f7 e6 8b 5e 0b 03  |`.F..V.. ....^..|
000000a0  c3 48 f7 f3 01 46 fc 11  4e fe 61 bf 00 00 e8 e6  |.H...F..N.a.....|
000000b0  00 72 39 26 38 2d 74 17  60 b1 0b be a1 7d f3 a6  |.r9&8-t.`....}..|
000000c0  61 74 32 4e 74 09 83 c7  20 3b fb 72 e6 eb dc a0  |at2Nt... ;.r....|
000000d0  fb 7d b4 7d 8b f0 ac 98  40 74 0c 48 74 13 b4 0e  |.}.}...._at_t.Ht...|
000000e0  bb 07 00 cd 10 eb ef a0  fd 7d eb e6 a0 fc 7d eb  |.........}....}.|
000000f0  e1 cd 16 cd 19 26 8b 55  1a 52 b0 01 bb 00 00 e8  |.....&.U.R......|
00000100  3b 00 72 e8 5b 8a 56 24  be 0b 7c 8b fc c7 46 f0  |;.r.[.V$..|...F.|
00000110  3d 7d c7 46 f4 29 7d 8c  d9 89 4e f2 89 4e f6 c6  |=}.F.)}...N..N..|
00000120  06 96 7d cb ea 03 00 00  20 0f b6 c8 66 8b 46 f8  |..}..... ...f.F.|
00000130  66 03 46 1c 66 8b d0 66  c1 ea 10 eb 5e 0f b6 c8  |f.F.f..f....^...|
00000140  4a 4a 8a 46 0d 32 e4 f7  e2 03 46 fc 13 56 fe eb  |JJ.F.2....F..V..|
00000150  4a 52 50 06 53 6a 01 6a  10 91 8b 46 18 96 92 33  |JRP.Sj.j...F...3|
00000160  d2 f7 f6 91 f7 f6 42 87  ca f7 76 1a 8a f2 8a e8  |......B...v.....|
00000170  c0 cc 02 0a cc b8 01 02  80 7e 02 0e 75 04 b4 42  |.........~..u..B|
00000180  8b f4 8a 56 24 cd 13 61  61 72 0b 40 75 01 42 03  |...V$..aar._at_u.B.|
00000190  5e 0b 49 75 06 f8 c3 41  bb 00 00 60 66 6a 00 eb  |^.Iu...A...`fj..|
000001a0  b0 4e 54 4c 44 52 20 20  20 20 20 20 0d 0a 4e 54  |.NTLDR      ..NT|
000001b0  4c 44 52 20 69 73 20 6d  69 73 73 69 6e 67 ff 0d  |LDR is missing..|
000001c0  0a 44 69 73 6b 20 65 72  72 6f 72 ff 0d 0a 50 72  |.Disk error...Pr|
000001d0  65 73 73 20 61 6e 79 20  6b 65 79 20 74 6f 20 72  |ess any key to r|
000001e0  65 73 74 61 72 74 0d 0a  00 00 00 00 00 00 00 00  |estart..........|
000001f0  00 00 00 00 00 00 00 00  00 00 00 ac bf cc 55 aa  |..............U.|

Yuriy