(My view only! I’m not a technician in the field. Answer regarding the questioners own answer and the comments appended there.)
It’s obviously a matter of interaction and cooperation: Windows (Did you already run 8.1 or 10 when using LO4?), the OLE implementation in the respective Windows and the usage of it by Mathtype and LibO as well. (I once heard of some problems with software using undocumented features of components by MS and their related… Didn’t you, too? And more recent versions of Win or of other software by MS often didn’t handle old software/related documents correcly even if from their own workbench.) Do you know someone using .doc or .docx [or .odt] with embedded Mathtype objects in MS Word Writer under the same system configuration? Of course, the issue may be caused by LibO. This is, however, not the only possibility. Why shouldn’t “dessci” be interested in the case? They may want to sell their next version to you. LibO won’t sell anything. They (dessci) might have technical insight enabling a shortcut with the OLE responsible at LibO…
Did you also consider that including OLE objects bound to Windows or Win-only-software may close in your documents - and yourself? LibO is dedicated to interoperability and portability - as far as not others hinder this impregnably. If you want to surrender so far, why not use MS Word Writer?