Bursty transmissions with X310?

Hi!

tl;dr: I can't seem to get the bursty transmissions to work with the
USRP Sink block. What am I missing?

Steps to reproduce: Run the following minimal-ish example, with two X310
devices:
https://github.com/BenWiederhake/demo_no_burst?tab=readme-ov-file#demo_no_burst
Expected behavior: The receiver sees the signal from the transmitter
only intermittently, the timing corresponding to the tx_sob and tx_eob
tags, just like the documentation [1] explains.
Actual behavior: The receiver sees a continuous signal from the
transmitter, nearly as if the USRP Sink block completely ignores my tags.

The Qt GUI Time Sink block in the flowgraph demonstrates that the tags
do indeed exist as intended.

I already checked the source code of the USRP Sink block [3], but I
don't fully grasp how it works or why "my" tags get ignored.

The `tags_demo` example program [3] from the GnuRadio source tree runs
without any errors and transmits a continuous signal into the air, but
no "timed bursts", contrary to its own description text.
However, the program hasn't been updated in several years, so perhaps it
doesn't work for unrelated reasons.
Can someone double-check this program?

Some troubleshooting:
- I tested various spelling variants of the tag keys/values.
- I already updated the USRP firmware image and rebooted all devices.
- I think I'm using mostly the newest software, so it's not a known
issue: GnuRadio 3.10.9.2 (Python 3.11.8), UHD_4.6.0.0+ds1-5+b2
- Ettus X310 rev 13, Daughterboard UBX-160 v2

What could I be doing wrong?

With regards,
Ben Wiederhake

[1] https://wiki.gnuradio.org/index.php/USRP_Sink#Bursty_Transmission
[2]
https://github.com/gnuradio/gnuradio/blob/main/gr-uhd/lib/usrp_sink_impl.cc#L459
[3]
https://github.com/gnuradio/gnuradio/blob/main/gr-uhd/examples/c%2B%2B/tags_demo.cc#L71