Same still happens on 4.3.0.12 on my XA2. It has a noticeable impact on battery life. I’m not sure if it always happens after having done a voice call. Restarting lipstick via the SFOS Utilities brings things back to normal.
I ran an strace, wrapped in time, for about 2 minutes when it happened. The phone was idle, display off, connected via SSH. The PID of offending voicecall-ui process was 20171 at that time.
[root@XperiaXA2 defaultuser]# time strace -p 20171 -c
strace: Process 20171 attached
^Cstrace: Process 20171 detached
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
45.74 0.145000 103 1399 7 poll
31.55 0.100000 17 5600 clock_gettime
22.71 0.072000 25 2800 2800 recvmsg
0.00 0.000000 0 8 restart_syscall
------ ----------- ----------- --------- --------- ----------------
100.00 0.317000 32 9807 2807 total
Command terminated by signal 2
real 1m 49.97s
user 0m 0.21s
sys 0m 1.02s
That are quite a lot syscall for an idle process, which, I guess, keeps at least one CPU constantly awake. After restarting the homescreen using Utilities, none of the voicecall-ui processes had a CPU usage of more than 0.0% according to htop.