BitcoinUnlimited: Pruning leaves too many blocks on disk

With prune=600 the node stores about 30 GB of blocks on disk.

I installed BU on a clean Debian environment, on the newly-created bu home folder:

bu@hwcharts:~$ wget 'https://www.bitcoinunlimited.info/downloads/bitcoinUnlimited-1.0.0-linux64.tar.gz'
bu@hwcharts:~$ tar -axf bitcoinUnlimited-1.0.0-linux64.tar.gz

and I created bitcoin.confbefore starting the client even once; it contains:

bu@hwcharts:~$ cat .bitcoin/bitcoin.conf
prune=600
excessiveblocksize=1000000
excessiveacceptdepth=12

then I started the client:

bu@hwcharts:~/bitcoinUnlimited-1.0.0/bin$ ./bitcoind --version
Bitcoin Unlimited Daemon version v1.0.0.1-b471620

bu@hwcharts:~/bitcoinUnlimited-1.0.0/bin$ nohup ./bitcoind &

and for two days the size of ~/.bitcoin kept rising up to 40 GB until block synching completed: (100% = 100 GB)

then I stopped the BU client with an unpolite pkill bitcoind, but ~/.bitcoin/debug.log recorded a smooth shutdown:

2017-02-06 22:26:03 UpdateTip: 30 of last 100 blocks have unexpected version. One example: 0x20000002
2017-02-06 22:26:21 tor: Thread interrupt
2017-02-06 22:26:21 torcontrol thread exit
2017-02-06 22:26:21 msghand thread interrupt
2017-02-06 22:26:21 opencon thread interrupt
2017-02-06 22:26:21 addcon thread interrupt
2017-02-06 22:26:21 scheduler thread interrupt
2017-02-06 22:26:21 net thread interrupt
2017-02-06 22:26:21 Shutdown: In progress...
2017-02-06 22:26:21 StopNode()
2017-02-06 22:26:21 Shutdown: done

then I restarted the client from the same path and with the same command as before. After the client restarted, the following was appended to the end of debug.log: https://pastebin.mozilla.org/8974271, and the disk usage inside ~/.bitcoin was

bu@hwcharts:~/.bitcoin$ du -h
1.9G    ./chainstate
67M     ./blocks/index
27G     ./blocks
29G     .

System details:

bu@hwcharts:~/.bitcoin$ uname -a
Linux hwcharts 2.6.32-042stab108.8 #1 SMP Wed Jul 22 17:23:23 MSK 2015 i686 GNU/Linux

bu@hwcharts:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/simfs      100G   37G   64G  37% /
tmpfs           205M   60K  205M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
devtmpfs         10M     0   10M   0% /dev
tmpfs           410M     0  410M   0% /run/shm

bu@hwcharts:~/.bitcoin$ free
             total       used       free     shared    buffers     cached
Mem:       2097152     446380    1650772          0          0     198332
-/+ buffers/cache:     248048    1849104
Swap:            0          0          0

bu@hwcharts:~/.bitcoin$ cat /etc/debian_version
8.6