Fax sending broken (after upgrading to raring?)

(Fix/Workaround included, see below)

Reproduce:
Try sending a fax using the fax printer from Evince, LibreOffice, etc.

Expected result:
Target phone number selection dialog should appear (from hplip).

Actual result:
Nothing visible happens / dialog doesn't appear.

OR

Reproduce:
Try sending a fax using the hp-sendfax utility. Cover page dialog appears, continue to the next step, add a PDF file (or anything else).

Expected result:
File should be listed in the file overview in hp-sendfax's dialog.

Actual result:
Returning from the file selection dialog does not trigger any visible action (selected file does not appear in the file list).

Debugging:
Saw this in the syslog:
hpcupsfax[12947]: common/utils.c 253: Failed to check directory [/var/log/hp/tmp] errno[2]

... so I created /var/log/hp/tmp (parent directory already existed).

Tried sending a fax again, saw this in the syslog:
hpcupsfax[31352]: prnt/hpijs/hpcupsfax.cpp 685: ERROR: Unable to open Fax output file - /var/log/hp/tmp/hplipfaxLog_sPUT65 for writing

Played with permissions on /var/log/hp/tmp until it worked. root:lp/775 sounds halfway sane and works for me. lp:.../755 would probably be okay as well.

Suggested fix:
Ensure that /var/log/hp/tmp gets pre-created with sane permissions or patch/configure hplip to use another path maybe (?).

I am not entirely sure when this bug got introduced. I had sent my last fax about two months ago, so it was certainly before the upgrade to raring.
I assume this bug is not printer-specific.

Similar issue in Fedora Core: https://bugs.launchpad.net/hplip/+bug/1055510

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: hplip 3.13.3-1
ProcVersionSignature: Ubuntu 3.8.0-22.33-generic 3.8.11
Uname: Linux 3.8.0-22-generic x86_64
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
Date: Mon Jun 3 22:50:14 2013
EcryptfsInUse: Yes
InstallationDate: Installed on 2011-06-17 (717 days ago)
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
Lpstat:
 device for Officejet_6500_E709a: hp:/net/Officejet_6500_E709a?zc=HPD8265E
 device for Officejet_6500_E709a_fax: hpfax:/net/Officejet_6500_E709a?zc=HPD8265E
MachineType: Gigabyte Technology Co., Ltd. GA-880GA-UD3H
MarkForUpload: True
Papersize: a4
PpdFiles:
 Officejet_6500_E709a: HP Officejet 6500 e709a, hpcups 3.13.3
 Officejet_6500_E709a_fax: HP Fax hpcups
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.8.0-22-generic root=UUID=93f6756c-a6cb-4dde-9875-e61e6daacefa ro quiet splash vt.handoff=7
SourcePackage: hplip
UpgradeStatus: Upgraded to raring on 2013-04-25 (39 days ago)
dmi.bios.date: 11/24/2010
dmi.bios.vendor: Award Software International, Inc.
dmi.bios.version: F7
dmi.board.name: GA-880GA-UD3H
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrF7:bd11/24/2010:svnGigabyteTechnologyCo.,Ltd.:pnGA-880GA-UD3H:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnGA-880GA-UD3H:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr:
dmi.product.name: GA-880GA-UD3H
dmi.sys.vendor: Gigabyte Technology Co., Ltd.