SolarMutex assert on adding an extension ?

If I try and install the extension from
https://bugs.freedesktop.org/show_bug.cgi?id=46447#c151
in master I get...

warn:vcl:29279:9:vcl/generic/app/geninst.cxx:116: CheckYieldMutex: 0!=9

which is
SalYieldMutex* pYieldMutex = mpSalYieldMutex;
if ( pYieldMutex->GetThreadId() != osl::Thread::getCurrentIdentifier() )
    return false;

causes this assert to trigger
assert(ImplGetSVData()->mpDefInst->CheckYieldMutex());                                              
                             

from DBG_TESTSOLARMUTEX(); in svl/source/notify/SfxBroadcaster.cxx's
SfxBroadcaster::AddListener

all the way from ExtensionCmdQueue::Thread::execute where everything is
happening in a thread to add an extension and so (because this is a
basic extension) BasicManagerRepository::getApplicationBasicManager is
called from the thread.

What should we do here ?

C.