Beamer document with unroll phantoms (with unroll, unroll compressed and unroll greyed it does not happen).

Within the unroll phantom an environment (say Theorem) with style Hanging Theorems not as the first item in the unroll.

If Preferences/Convert/Pdf/Expand beamer slides is ticked export to pdf works fine. If it is not ticked, export to pdf causes TeXmacs to crash with the error message below.

TeXmacs 2.1
Ubuntu 20.04.3

Throwing segmentation fault
-------------------------------------------------
Error message:
  segmentation fault

System information:
  TeXmacs version  : 2.1
  Built by         : abuild
  Building date    : Tue Jun 22 11:58:17 UTC 2021
  Operating system : linux-gnu
  Vendor           : pc
  Processor        : @CONFIG_HOST_CPU@
  Crash date       : Thu 25 Nov 2021 14:07:12 CET

Editor status:
  Root path          : [ 2 ]
  Current path       : [ 2, 0, 0, 1, 0, 1 ]
  Shifted path       : [ 2, 0, 0, 1, 0, 1 ]
  Physical selection : [] -- []

Backtrace of C++ stack:
  texmacs.bin : () + 0xed5206
  texmacs.bin : () + 0x420100
  /usr/lib/x86_64-linux-gnu/libc.so.6 : () + 0x46210
  texmacs.bin : () + 0xcced83
  texmacs.bin : () + 0xa3c65a
  texmacs.bin : () + 0x45d7ba
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d295
  texmacs.bin : () + 0x45d4ab
  texmacs.bin : () + 0x6ccf49
  texmacs.bin : () + 0x6ca638
  texmacs.bin : () + 0x9b4de2
  texmacs.bin : () + 0x109994f
  texmacs.bin : () + 0x1098a0e
  texmacs.bin : () + 0x1096c82
  texmacs.bin : () + 0x10ee27c
  texmacs.bin : () + 0x10edeb0
  texmacs.bin : () + 0x10ee152
  texmacs.bin : () + 0xa3a1bd
  texmacs.bin : () + 0xc05a8a
  texmacs.bin : () + 0xd6366f
  texmacs.bin : () + 0xd639e3
  texmacs.bin : () + 0xd645aa
  texmacs.bin : () + 0x30b6a4
  texmacs.bin : () + 0xba5de8
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QMetaObject::activate(QObject*, int, int, void**) + 0x7d0
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QTimer::timeout(QTimer::QPrivateSignal) + 0x3e
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QObject::event(QEvent*) + 0x1d5
  /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5 : QApplicationPrivate::notify_helper(QObject*, QEvent*) + 0x86
  /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5 : QApplication::notify(QObject*, QEvent*) + 0x330
  texmacs.bin : () + 0xba5500
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QCoreApplication::notifyInternal2(QObject*, QEvent*) + 0x18a
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QTimerInfoList::activateTimers() + 0x3d0
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : () + 0x2de19c
  /lib/x86_64-linux-gnu/libglib-2.0.so.0 : g_main_context_dispatch() + 0x27d
  /lib/x86_64-linux-gnu/libglib-2.0.so.0 : () + 0x52400
  /lib/x86_64-linux-gnu/libglib-2.0.so.0 : g_main_context_iteration() + 0x33
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 0x65
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 0x12b
  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 : QCoreApplication::exec() + 0x96
  texmacs.bin : () + 0x2868f5
  texmacs.bin : () + 0x10afb73
  texmacs.bin : () + 0x11067fe
  texmacs.bin : () + 0x10edeb0
  texmacs.bin : () + 0x1106e17
  texmacs.bin : () + 0x1106f04
  texmacs.bin : () + 0x10ec16a
  texmacs.bin : () + 0x10afcfb
  texmacs.bin : () + 0x25f0a6
  /usr/lib/x86_64-linux-gnu/libc.so.6 : __libc_start_main() + 0xf3
  texmacs.bin : () + 0x284ece

-------------------------------------------------
terminate called after throwing an instance of 'string'