Applications stop in the middle of start process

[stippi]

I've only seen this in recent revisions (currently running hrev28334), but I cannot say when it started. Sometimes, when I launch applications, they get a Deskbar entry but open no window. This also affects very simple applications, like a preflet. Printing the stack crawl in KDL for the application thread (in my case here the only thread of the application yet) gives this:

<kernel_x86> context_switch(thread*: 0x81a13000, thread*: 0x80110bf0) + 0x003c
<kernel_x86> simple_reschedule() + 0x029f
<kernel_x86>:switch_sem_etc + 0x0319
<kernel_x86>:acquire_sem_etc + 0x0026
<kernel_x86>:_get_port_message_info_etc + 0x012e
<kernel_x86>:port_buffer_size_etc + 0x0025
<kernel_x86>:user_port_buffer_size_etc + 0x008d
<kernel_x86>:handle_syscall + 0x00af
user iframe at 0x83795fa8 (end = 0x83796000)
 eax 0xc3           ebx 0x5112fc    ecx 0x3f        edx 0xbd02f
 esi 0xffffffff     edi 0x7fffffff  ebp 0x7ffeebcc  esp 0x83795fdc
 eip 0xffff0102  eflags 0x216  user esp 0x7ffeeba0
 vector: 0x63, error code: 0x0
<commpage>:commpage_syscall + 0x0002
<libbe.so>:__c1__Q38BPrivate11BLooperList12FindPortPredRQ38BPrivate11BLooperList10LooperData (nearest) + 0x015b
[*** READ FAULT at 0xffffffff, pc: 0x800d7f83 ***]

I have no idea what recent change could have caused this. Looks like the thread is waiting for a reply, but there were no app_server or registrar changes recently, were there?