Firmware update hangs on Gen 8.1 when update is a 'noop'

When using ironic manual cleaning to update firmware on a Gen 8.1 device, if the firmware has already been updated to the requested version, then the update hangs. The ilo firmware is 2.72, and the hardware is a BL460c blade. I can see from ironic debug logs that the firmware update has started, but the node remains in the cleaning state.

2020-01-14 17:19:37.237 28457 DEBUG ironic.drivers.modules.ilo.management [req-cea63c24-f152-4216-96f8-0da49f28cf0e - - - - -] Firmware update for /tmp/cde00ab6-baf4-4d3d-a7ec-2862c6842351_ilo4_272.bin on node: c1ea7dd2-f01a-43d1-b6f8-f948dabda48b ... in progress update_firmware /usr/lib/python2.7/site-packages/ironic/drivers/modules/ilo/management.py:4
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I tried resetting the ilo, to see if this would trigger the wait conditions in the proliantutils library. It did not help.

Seen with proliantutils 2.4.0.