Failures on Backing up of Data with Large WAL size on 1.8.1 throws error : Database disk image is malformed

Backup fails for files w/ large size WAL[ 5M plus]. Backup is successful for smaller WAL sizes [default :1000].

Steps to Reproduce this issue
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Load 1M of data : [/opt/couchbase/bin/memcachetest -h localhost:11211 -i 1000000 -M 1024 -K cb_2 -l ]
Run a backup of the data [ while database is online] : sudo -su couchbase /opt/couchbase/bin/cbbackup /opt/couchbase/var/lib/couchbase/data/default-data/default /tmp/rev7

Errors
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..
Backup of default done, check integrity now
ok
Vacuum of default done
Backup of default-0.mb done, check integrity now

• • • in database main ***
      On tree page 395901 cell 3: 2nd reference to page 395903
      On tree page 426067 cell 0: 2nd reference to page 410862
      On tree page 426067 cell 1: 2nd reference to page 410863
      .
      .
      .
      .

On tree page 461483 cell 2: 2nd reference to page 462480
On tree page 467250 cell 1: 2nd reference to page 440802
On tree page 472512 cell 1: 2nd reference to page 471560
On tree page 358585 cell 1: 2nd reference to page 358586
On tree page 474942 cell 1: 2nd reference to page 473623
Page 491172: btreeInitPage() returns error code 11
On tree page 485795 cell 89: Child page depth differs
Page 491173: btreeInitPage() returns error code 11
Page 491175: btreeInitPage() returns error code 11
On tree page 336498 cell 0: 2nd reference to page 336497
On tree page 385778 cell 2: 2nd reference to page 385777
On tree page 394903 cell 1: 2nd reference to page 394901
On tree page 427473 cell 1: 2nd reference to page 427474
On tree page 436046 cell 0: 2nd reference to page 436045
On tree page 437909 cell 0: 2nd reference to page 437907
On tree page 444827 cell 1: 2nd reference to page 444046
On tree page 467244 cell 0: 2nd reference to page 471558
On tree page 483494 cell 0: 2nd reference to page 469621
On tree page 376439 cell 1: 2nd reference to page 376440
On tree page 376453 cell 1: 2nd reference to page 376412
On tree page 399713 cell 2: 2nd reference to page 399714
On tree page 411158 cell 1: 2nd reference to page 412526
On tree page 426543 cell 0: 2nd reference to page 362805
Page 491168: btreeInitPage() returns error code 11
On tree page 482558 cell 86: Child page depth differs
Page 491169: btreeInitPage() returns error code 11
Page 491170: btreeInitPage() returns error code 11
Page 491171: btreeInitPage() returns error code 11
On tree page 385413 cell 1: 2nd reference to page 385411
On tree page 407221 cell 1: 2nd reference to page 407222
On tree page 416240 cell 1: 2nd reference to page 416241
On tree page 426539 cell 1: 2nd reference to page 427355
On tree page 430171 cell 2: 2nd reference to page 429186
On tree page 433173 cell 0: 2nd reference to page 433172
On tree page 434095 cell 1: 2nd reference to page 434096
On tree page 439678 cell 0: 2nd reference to page 439677
On tree page 479441 cell 1: 2nd reference to page 479442
Page 491162: btreeInitPage() returns error code 11
On tree page 487719 cell 79: Child page depth differs
Page 491163: btreeInitPage() returns error code 11
Page 491166: btreeInitPage() returns error code 11
On tree page 376307 cell 1: 2nd reference to page 376308
On tree page 385403 cell 1: 2nd reference to page 388156
On tree page 428240 cell 1: 2nd reference to page 428241
On tree page 430165 cell 3: 2nd reference to page 430166
Error: database disk image is malformed
Vacuum of default-3.mb done