If you have Office running non-isolated, starting it in isolation will result in crash. The culprit here is mutex, who could have thought. Office tries to create (or open) mutex named 5CAC3FAB-87F0-4750-984D-D50144543427Office-VERXX (where VERXX depends on version like VER15 or VER16) with MUTEX_ALL_ACCESS access right. If this mutes was already created by non-isolated instance, isolated Office will fail to open it... you guessed it right, because of isolation and blocked access. Failure to open mutex will result in crash. So much for the mutex. When it was discovered, it was still unpatched. Haven't checked since then. So beware, even mutexes can crash programs.
