I've got a Mac OS 26 guest running on Mac OS 26 host. The guest has Sharing > Share Custom Mac Folders With Macos enabled. When an app in the guest accesses a text file via "My Shared Files", it appears that the guest caches the contents of that file and doesn't invalidate the cache when it gets changed on the host -- that is, the guest doesn't see changes to the text file until the guest restarts. If the guest accesses host files using Network and shared network folders, then the guest sees the most recent version of the host files, as expected. Is this a bug?
I'm experiencing the same problem using a macOS 15 host and a macOS 26 guest under Parallels Desktop 26. When I modify a file on the host side the guest sees that the file size has changed but the contents have not. If the file size grows on the host the guest sees the old bytes followed by random garbage.
Just did a few more experiments. I opened Terminal windows in both the guest and host and used the command line to echo strings into a text file. When I alter the contents of a file on the guest side (macOS 26) the host sees the new contents. When I alter the contents on the host side (macOS 15) the guest sees the new metadata (file length) but not new contents. If the file expands on the host the guest sees that the file is longer but the contents are stale and padded out with zeros. Parallels Version 26.3.0 (57392) on an Apple Studio running Sequoia 15.7.4, guest is Tahoe 26.3.1. I'm trying to open a ticket with support but since I don't do social media this is not easy.
