Eu também experimento isso com um servidor hospedado em nossa universidade. Parece ser o modo como o Office administra a solicitação de um arquivo do Office a partir da Web. Servidores que não oferecem WebDAV ou outra capacidade para os usuários salvarem arquivos no servidor devem ter alguns verbos / extensões desabilitados conforme descrito.
O artigo 2019105 da Base de Dados de Conhecimento da Microsoft oferece as melhores informações sobre por que isso ocorre e as opções sugeridas para solucioná-lo. Artigo da base de conhecimento: link
Causa:
When Internet Explorer opens an Office document, the appropriate Office application is started with the path of the document. The Office application then tries to access the document directly from the server. This differs from other browsers and other file types. Most browsers download the file and call the application to open the file from the local cache. However, when this occurs, if the opened file is changed and saved, the changes are only made to the local copy and not to the server copy.
To establish the richest experience possible, the first thing that the Office application does is communicate with the server to determine the server type and what web authoring protocol is available. The application does this by making an OPTIONS request directly to the server.
As a new process accessing the server, the Office application is required to renegotiate authentication. This method is more secure than a method in which the new process uses an existing authentication that was established by the browser.
The article’s recommendation is that when users will not be attempting to save files back to the server directly addressing this should be completed on the server side. Specifically disabling the support of OPTIONS and PROPFIND verb/extensions.