Nine track file marks, Burroughs

Folks, I've now seen two Burroughs tapes where some of the expected file marks between labels and file data were apparently missing. I think a reasonable description of these is "Burroughs/Unisys B6x00 'Library/Maintenance' tapes with ANSI-69 labels" Reading drive is a Cipher GCR Cachetape with SCSI interface The one I read yesterday read in streaming mode and reported no read errors. I tried re-reading it today, and it read in start-stop mode, but still didn't have the missing file marks. (It also encountered a few errors, and eventually ended up sticking to the head, this time. Guess that bake cycle was a one-shot, which isn't a surprise.) This tape is a "Burroughs Series 7 / 100% Tested / 3200 FCI" 1200 foot reel written at 1600 BPI in 1986. Here's the beginning of the tape: file 1 record 1 size 80 00000000: e5 d6 d3 f1 f0 f3 f6 f1 f3 f0 40 d7 d9 d6 c7 d9 VOL1036130 PROGR 00000010: c1 d4 40 40 40 40 40 40 40 40 40 40 f6 f5 f3 f0 AM 6530 00000020: f3 f0 f5 f0 f3 40 40 40 40 40 40 40 40 40 40 40 30503 00000030: 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 00000040: 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 f1 1 file 1 record 2 size 80 00000000: c8 c4 d9 f1 c6 c9 d3 c5 f0 f0 f0 40 40 40 40 40 HDR1FILE000 00000010: 40 40 40 40 40 d7 d9 d6 c7 d9 c1 f0 f0 f0 f1 f0 PROGRA00010 00000020: f0 f0 f1 f0 f0 f0 f1 f0 f0 40 f8 f6 f2 f0 f2 40 001000100 86202 00000030: f8 f6 f2 f3 f2 40 f0 f0 f0 f0 f0 f0 f0 f0 f0 f0 86232 0000000000 00000040: f0 f0 f0 40 c1 f9 40 40 40 40 40 40 40 40 40 40 000 A9 file 1 record 3 size 80 00000000: c8 c4 d9 f2 e4 f0 f1 f0 f2 f4 f0 f1 f0 f2 f4 f3 HDR2U01024010243 00000010: f0 f1 f0 f1 f0 f0 f0 f0 f3 f0 f0 f0 f0 f0 f0 f0 0101000030000000 00000020: f0 f0 f0 f0 f0 f6 f4 f0 f0 f1 f3 40 f0 f0 f6 f4 00000640013 0064 00000030: 40 40 f0 f6 40 40 40 40 40 40 40 40 40 40 40 40 06 00000040: 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 file 1 record 4 size 2070 00000000: 40 00 00 00 00 01 00 00 00 00 00 00 12 03 03 04 ............... ...etc. Is oddness with file marks something others have seen with Burroughs tapes? Something the Cipher drive is known for? Moon phase? Incorrect fifth digit of my SSN? I've not had this missing file mark problem with tapes written on other vendors systems - Prime, IBM, DEC. Cluebats appreciated. De