"Engineering has determined that this issue behaves as intended based on the following information:
when PowerPoint is opening an older file (.ppt), it issues an SMB request to update the "Last Write Time" timestamp of the file. But the SMB server only allows the file owner to update the "Last Write Time" timestamp of a file.
This means only the file owner can open an older .ppt file with PowerPoint while other group members will get Access Denied.
When PowerPoint opens newer files (.pptx), it creates a temporary file and makes changes such as "Last Write Time" timestamp to the temporary file (which is owned by the current user), then it renames the file to the original name. This is why you don't see the issue with new format files an PowerPoint.
The ACLs that you configured are still important because they allow other group users to access your newer files (.pptx). But unfortunately ACLs cannot allow other group users to update timestamps (such as "Last Write Time").
Sorry for the inconvenience with older PowerPoint files, but I believe the server is behaving correctly.
If you have questions regarding the resolution of this issue, please update your bug report with them.
We are now closing this bug report."