Pin-pad on SPR332 smartcard reader does not work under OSX

[Niobos]

Hi,

I'm trying to get my smartcard to work under Mac OS X (OSX 10.9,
Mavricks) with GnuPG 2.1.1. It mostly works out of the box, but there is
one minor issue that I can't get to work: the pinpad on my SmartCard
reader (SPR332). (Pin is asked by the pinentry program, not by the card
reader itself)

I've tried to debug this myself. This is what I found:
I can see scdaemon doing pcsc_vendor_specific_init(), but failing:

> pcsc_vendor_specific_init: GET_FEATURE_REQUEST failed: 65538


How should I proceed to get this to work? Is it even supposed to work
under OSX? What additional info do you need?

Additional info: Card reader & card work fine under Linux; Card is the
ZeitControl card from g10code.com


Thanks in advance,
Niobos