Swayidle doesn't actually register a sleep inhibit

[rassouly]

Sway version: sway version 1.0-beta.2-100-gbb5b168b (Jan 5 2019, branch 'master')
I start swayidle with the following command

swayidle -d before-sleep 'echo "42"' 

And I get the following log when I run systemctl suspend afterwards

2019-01-06 12:33:32 - [sway/swayidle/main.c:357] Got before-sleep
2019-01-06 12:33:32 - [sway/swayidle/main.c:270] Command: echo "42"
2019-01-06 12:33:32 - [sway/swayidle/main.c:321] Setup sleep lock: echo "42"
2019-01-06 12:33:32 - [sway/swayidle/main.c:108] Got sleep lock: 9
2019-01-06 12:33:50 - [sway/swayidle/main.c:123] PrepareForSleep signal received 1
2019-01-06 12:33:50 - [sway/swayidle/main.c:53] Cmd exec echo "42"
2019-01-06 12:33:50 - [sway/swayidle/main.c:70] Spawned process echo "42"
2019-01-06 12:33:50 - [sway/swayidle/main.c:141] Prepare for sleep done
42
2019-01-06 12:33:56 - [sway/swayidle/main.c:81] Releasing sleep lock 9
2019-01-06 12:33:56 - [sway/swayidle/main.c:123] PrepareForSleep signal received 0
2019-01-06 12:33:56 - [sway/swayidle/main.c:108] Got sleep lock: 9

Even though the logs look like swayidle was able to acquire the lock, the lock is released after the system has resumed (look at the timestamps). Moreover, when I run systemd-inhibit (which lists all the inhibitors currently registered), I can't see swayidle

$ systemd-inhibit --list
WHO            UID USER PID   COMM           WHAT  WHY                                       MODE 
NetworkManager 0   root 445   NetworkManager sleep NetworkManager needs to turn off networks delay
UPower         0   root 27834 upowerd        sleep Pause device polling                      delay

2 inhibitors listed.

I looked at the logind.conf man page and couldn't find any setting that might be relevant to this issue. Any ideas?