Windows Media Encoder 9 installation randomly hangs at the progress bar with RtlpWaitForCriticalSection, netapi logging, no CPU load

0.4.14-dev-1296-g56aa513 gcc 4.7.2 dbg linux build.
We recently did improve a bit on the setup of
"Windows Media Encoder 9" from rapps.
(older CORE-16350 is fixed now)

Expected result
2k3sp2_wmeStup_ok.webm

Observed result
Currently the setup hangs with 0% CPU load at a progress bar.
The last logging is

fixme:(dll/win32/netapi32/wksta.c:335) Level 1 processing is partially implemented

Not sure, whether it is related.
0.4.14-dev-1296-g56aa513_WMEsetupHangs.log
0.4.14-dev-1296-g56aa513_WMEsetupHangs.webm

Stacksampling (recurrently breaking into the debugger) does not reveal anything interesting, only (HalProcessorIdle), so will not help us here.