I had it happen just now and I grabbed the process with GDB and stole a backtrace.  Not sure if this is telling, but I thought I'd safe it here :-)

(gdb) bt
#0  0x00007fe4539118bd in nanosleep () at ../sysdeps/unix/syscall-template.S:82
#1  0x00007fe453b8cd32 in g_usleep (microseconds=<optimized out>)
    at /build/buildd/glib2.0-2.29.18/./glib/gtimer.c:253
#2  0x00007fe454d68152 in ?? () from /usr/lib/libedataserver-1.2.so.15
#3  0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#4  0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
#5  0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#6  0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#7  g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#8  0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#9  0x00007fe453b64829 in g_main_context_iteration (context=0x7fe444001f40, 
    may_block=0) at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3152
#10 0x00007fe454d6815b in ?? () from /usr/lib/libedataserver-1.2.so.15
#11 0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#12 0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
---Type <return> to continue, or q <return> to quit---
#13 0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#14 0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#15 g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#16 0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#17 0x00007fe453b64829 in g_main_context_iteration (context=0x7fe444001f40, 
    may_block=0) at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3152
#18 0x00007fe454d6815b in ?? () from /usr/lib/libedataserver-1.2.so.15
#19 0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#20 0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
#21 0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#22 0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#23 g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#24 0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
---Type <return> to continue, or q <return> to quit---
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#25 0x00007fe453b64829 in g_main_context_iteration (context=0x7fe444001f40, 
    may_block=0) at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3152
#26 0x00007fe454d6815b in ?? () from /usr/lib/libedataserver-1.2.so.15
#27 0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#28 0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
#29 0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#30 0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#31 g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#32 0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#33 0x00007fe453b64829 in g_main_context_iteration (context=0x7fe444001f40, 
    may_block=0) at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3152
#34 0x00007fe454d6815b in ?? () from /usr/lib/libedataserver-1.2.so.15
#35 0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#36 0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
---Type <return> to continue, or q <return> to quit---
#37 0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#38 0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#39 g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#40 0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#41 0x00007fe453b64829 in g_main_context_iteration (context=0x7fe444001f40, 
    may_block=0) at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3152
#42 0x00007fe454d6815b in ?? () from /usr/lib/libedataserver-1.2.so.15
#43 0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#44 0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
#45 0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#46 0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#47 g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#48 0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
---Type <return> to continue, or q <return> to quit---
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#49 0x00007fe453b64829 in g_main_context_iteration (context=0x7fe444001f40, 
    may_block=0) at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3152
#50 0x00007fe454d6815b in ?? () from /usr/lib/libedataserver-1.2.so.15
#51 0x00007fe454d6b978 in e_gdbus_proxy_call_sync_boolean__void ()
   from /usr/lib/libedataserver-1.2.so.15
#52 0x00007fe455adfefc in ?? () from /usr/lib/libecal-1.2.so.10
#53 0x00007fe455ae022e in ?? () from /usr/lib/libecal-1.2.so.10
#54 0x00007fe453b63e5d in g_main_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:2442
#55 g_main_context_dispatch (context=0x7fe444001f40)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3011
#56 0x00007fe453b64658 in g_main_context_iterate (context=0x7fe444001f40, 
    block=<optimized out>, dispatch=1, self=<optimized out>)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3089
#57 0x00007fe453b64b92 in g_main_loop_run (loop=0x1774020)
    at /build/buildd/glib2.0-2.29.18/./glib/gmain.c:3297
#58 0x0000000000404348 in ?? ()
#59 0x00007fe45358430d in __libc_start_main (main=0x403ef0, argc=1, 
    ubp_av=0x7fff188acd98, init=<optimized out>, fini=<optimized out>, 
    rtld_fini=<optimized out>, stack_end=0x7fff188acd88) at libc-start.c:226
---Type <return> to continue, or q <return> to quit---
#60 0x0000000000404515 in ?? ()
#61 0x00007fff188acd88 in ?? ()
#62 0x000000000000001c in ?? ()
#63 0x0000000000000001 in ?? ()
#64 0x00007fff188aea15 in ?? ()
#65 0x0000000000000000 in ?? ()
(gdb)