Crash when closing second app

Quoting Daniel d'Andrada

I can launch and close a single app at a time, no problem.
But if I launch a second one (having therefore two apps running simultaneously) I get a crash when switching between them (with right edge gesture) or trying to close one of them (through the dash thumbnail).

Got this stacktrace:

#0 __libc_do_syscall () at
../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:44
#1 0x40b195fe in __GI_raise (sig=sig@entry=6) at
../nptl/sysdeps/unix/sysv/linux/raise.c:56
#2 0x40b1be1a in __GI_abort () at abort.c:90
#3 0x40a937ac in __gnu_cxx::__verbose_terminate_handler () at
../../../../src/libstdc++-v3/libsupc++/vterminate.cc:95
#4 0x40a921cc in __cxxabiv1::__terminate (handler=<optimized out>) at
../../../../src/libstdc++-v3/libsupc++/eh_terminate.cc:38
#5 0x40a91676 in __cxa_call_terminate (ue_header=0x1074f60) at
../../../../src/libstdc++-v3/libsupc++/eh_call.cc:54
#6 0x40a91f06 in __cxxabiv1::__gxx_personality_v0 (state=<optimized
out>, ue_header=0x1074f60, context=<optimized out>)
    at ../../../../src/libstdc++-v3/libsupc++/eh_personality.cc:670
#7 0x401747d6 in unwind_phase2 (ucbp=ucbp@entry=0x1074f60,
vrs=vrs@entry=0x4fddaa24) at ../../../src/libgcc/unwind-arm-common.inc:294
#8 0x401749a6 in __gnu_Unwind_Resume (ucbp=0x1074f60,
entry_vrs=0x4fddaa24) at ../../../src/libgcc/unwind-arm-common.inc:502
#9 0x401751ae in _Unwind_Resume () at
../../../src/libgcc/config/arm/libunwind.S:344
#10 0x41076bd2 in mir::frontend::SessionMediator::~SessionMediator() ()
from /usr/lib/arm-linux-gnueabihf/libmirserver.so.1
#11 0x40bd3000 in ?? () from /lib/arm-linux-gnueabihf/libc.so.6
Cannot access memory at address 0x2
#12 0x40bd3000 in ?? () from /lib/arm-linux-gnueabihf/libc.so.6
Cannot access memory at address 0x2