[EntBackupRestore] panic found while taking backup with parallel CRUD

I was trying to execute the following scenario manually:

3 incremental backup with parallel CRUD, rebalance in, 2 incremental backup with parallel CRUD, 1 merge
3 incremental backup with parallel CRUD, rebalance in, 2 incremental backup with parallel CRUD, 1 merge
merge from 1 & 2 - restore to dest cluster and verify merge

I created 5000 items using cbworkloadgen and took 1st incr backup - started pillowfight on the cluster for parallel CRUD with 50% reads and 50% updates - while ops were happening in parallel tried to take 2nd backup - backup failed with this message on the terminal:

[root@node3-cb450-testing-centos6 bin]# ./cbbackupmgr backup -c http://10.111.150.101:8091 -u Administrator -p password -a /tmp -r backup

Backing up to 2017-06-07T14_54_09.240831229Z
Copying at 2.58MB (>24h remaining)

List shows 0 items in second backup:

[root@node3-cb450-testing-centos6 bin]# ./cbbackupmgr list -a /tmp -r backup
Size Items Name
104.06MB - + backup
54.25MB - + 2017-06-07T14_52_53.21329833Z
54.25MB - + default
364B 0 bucket-config.json
54.25MB 5000 + data
54.25MB 5000 shard_0.fdb
2B 0 full-text.json
4B 0 gsi.json
2B 0 views.json
49.81MB - + 2017-06-07T14_54_09.240831229Z
49.81MB - + default
364B 0 bucket-config.json
49.81MB 0 + data
49.81MB 0 shard_0.fdb
2B 0 full-text.json
4B 0 gsi.json
2B 0 views.json

As result of CRUD the bucket has 6000 items which is not backed up in 2nd incr backup - following panic is seen in logs:

panic: strings: negative Repeat count

goroutine 14 [running]:

strings.Repeat(0x7c1108, 0x1, 0xfffffffffffffffd, 0xc4204c8210, 0xad)

	/home/couchbase/.cbdepscache/exploded/x86_64/go-1.8.1/go/src/strings/strings.go:432 +0x258

main.progressBar(0xd7ff, 0xd415, 0xcc, 0x1, 0xc420111ce8, 0x7, 0x0, 0xc4202b01a0)

	/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/backup/cmd/cbbackupmgr/progress_bar.go:169 +0x316

main.startProgressBar(0x7c431b, 0xd, 0xc42012c560, 0x1e, 0xc42001fb40)

	/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/backup/cmd/cbbackupmgr/progress_bar.go:88 +0x7ba

main.(*BackupContext).Run.func1(0xc42001fb40, 0xc420142260)

	/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/backup/cmd/cbbackupmgr/backup.go:89 +0x51

created by main.(*BackupContext).Run

	/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/backup/cmd/cbbackupmgr/backup.go:91 +0x433

Attaching logs