I've recently noticed that block data is not published via zmq during the initial sync (but transaction data is).

Is that something to be expected, or could it be a misconfiguration of my node (or even, but less likely, a bug)?

Here are some logs:

zmq being set up:

2019-09-23T16:34:40Z zmq: version 4.3.2
2019-09-23T16:34:40Z zmq: Initialize notification interface
2019-09-23T16:34:40Z zmq: Outbound message high water mark for pubhashblock at tcp://127.0.0.1:28332 is 1000
2019-09-23T16:34:40Z zmq: Notifier pubhashblock ready (address = tcp://127.0.0.1:28332)
2019-09-23T16:34:40Z zmq: Outbound message high water mark for pubhashtx at tcp://127.0.0.1:28333 is 1000
2019-09-23T16:34:40Z zmq: Notifier pubhashtx ready (address = tcp://127.0.0.1:28333)
2019-09-23T16:34:40Z zmq: Reusing socket for address tcp://127.0.0.1:28332
2019-09-23T16:34:40Z zmq: Outbound message high water mark for pubrawblock at tcp://127.0.0.1:28332 is 1000
2019-09-23T16:34:40Z zmq: Notifier pubrawblock ready (address = tcp://127.0.0.1:28332)
2019-09-23T16:34:40Z zmq: Reusing socket for address tcp://127.0.0.1:28333
2019-09-23T16:34:40Z zmq: Outbound message high water mark for pubrawtx at tcp://127.0.0.1:28333 is 1000
2019-09-23T16:34:40Z zmq: Notifier pubrawtx ready (address = tcp://127.0.0.1:28333)

Block data being received and tx data published via zmq:

2019-09-23T16:38:13Z Requesting block 000000000021b9e7a7685ce88e023584eb5cf3e71201efd0b981e423b2143546 (77744) peer=2
2019-09-23T16:38:13Z sending getdata (37 bytes) peer=2
2019-09-23T16:38:13Z received: block (375 bytes) peer=2
2019-09-23T16:38:13Z zmq: Publish hashtx 986b91c3b2c3955ca503bf5d2aaf65a0b87c5c0639e74ca365d5e14a24466475
2019-09-23T16:38:13Z received block 000000000035052cb4f92ee3f94f60ce179cf9b6327f2f77bf51b31d7fe56488 peer=2
2019-09-23T16:38:13Z zmq: Publish rawtx 986b91c3b2c3955ca503bf5d2aaf65a0b87c5c0639e74ca365d5e14a24466475
2019-09-23T16:38:13Z WriteBatch memory usage: db=txindex, before=0.0MiB, after=0.0MiB
2019-09-23T16:38:13Z   - Load block from disk: 0.00ms [0.00s]
2019-09-23T16:38:13Z     - Sanity checks: 0.03ms [0.00s (0.02ms/blk)]
2019-09-23T16:38:13Z     - Fork checks: 0.06ms [0.00s (0.06ms/blk)]
2019-09-23T16:38:13Z       - Connect 2 transactions: 0.10ms (0.048ms/tx, 0.096ms/txin) [0.00s (0.08ms/blk)]
2019-09-23T16:38:13Z     - Verify 1 txins: 0.14ms (0.142ms/txin) [0.01s (0.11ms/blk)]
2019-09-23T16:38:13Z     - Index writing: 0.24ms [0.01s (0.15ms/blk)]
2019-09-23T16:38:13Z     - Callbacks: 0.04ms [0.00s (0.03ms/blk)]
2019-09-23T16:38:13Z   - Connect total: 0.63ms [0.02s (0.44ms/blk)]
2019-09-23T16:38:13Z   - Flush: 0.04ms [0.00s (0.03ms/blk)]
2019-09-23T16:38:13Z   - Writing chainstate: 0.03ms [0.00s (0.02ms/blk)]
2019-09-23T16:38:13Z Blockpolicy estimates updated by 0 of 0 block txs, since last block 0 of 0 tracked, mempool map size 0, max target 0 from current
2019-09-23T16:38:13Z UpdateTip: new best=000000000035052cb4f92ee3f94f60ce179cf9b6327f2f77bf51b31d7fe56488 height=77713 version=0x00000001 log2_work=53.823656 tx=110490 date='2010-09-02T15:05:32Z' progress=0.000244 cache=0.0MiB(215txo)

bitcoin.conf:

# [debug]
debug=1
logips=1

# [blockchain]
txindex=1

# [ZMQ]
zmqpubhashblock=tcp://127.0.0.1:28332
zmqpubrawblock=tcp://127.0.0.1:28332
zmqpubhashtx=tcp://127.0.0.1:28333
zmqpubrawtx=tcp://127.0.0.1:28333

It works fine in regtest and testnet3 when receiving blocks out of the initial sync.