Dual boot: Ubuntu 18.10 with Windows 10 1809. (Windows came first.)

A lot of my Windows folders became read-only, when accessed from Windows. This is true of Dropbox, but not just Dropbox. Lots of locations.
While in Linux, I accessed a lot of folders on the Windows partition, and also on a second hard disk containing personal data. Maybe that messed things up, as far as Windows is concerned?
If not, what might be the cause?

It did not help to change the properties of these folders, they go right back to read-only. I also tried sharing them with myself, but that didn't help, either.

I suppose this is a strange place to troubleshoot a Windows problem, but I think it was caused by the Linux double-boot, because this never happened to me before, and I have already broken just about everything possible in Windows.

Did you actually SHUT DOWN Windows, or did you hibernate?? Because that puts Windows partitions in a different state.

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I don't do hibernation. When I switch between Windows and Linux, I always reboot.

So you actually shut the machine down, by selecting "Shutdown" in Windows? A 'warm' reboot may also be an issue with partition state, but that's a guess. Windows doesn't play well with others.

How are you browsing/accessing those folders? Are you mounting the Windows partition, and if so, how? The ntfs-3g/fuse tools allow read/write, but other utilities may not.

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I guess you would call it a "warm" reboot. I thought that reboot tells the OS to make a fresh start.
I accessed the Windows folders by means of the native Ubuntu file manager, I think it is called Nautilus.
I noticed sometimes that locations became mounted, but that happened automatically. I honestly don't even understand what "mounting" means, in the linux sense of the term.

By default Windows uses fast startup which is a hybrid sleep mode. Ubuntu should detect if the filesystem is hibernated and display a warning message. If you have ignored the warning and actually mounted your Windows filesystem anyway that might of caused your problems.

If you have disabled fast startup mode then please ignore the above.

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Right. That is why I do a reboot when switching from Windows to Linux, because it does not use fast startup.

I did not see warnings in Linux for most locations I tried to access, and those that were restricted, I couldn't get into them.

I googled around a little, and I saw people were complaining of read-only after a Windows update.
So I restored an earlier system image, but the issue did not reappear after checking for available Windows updates. So I assume that is not the cause.

So if you guys are not coming up with a pat answer, then let's just assume it happened because one time I forgot to do a proper reboot, and Windows was in a sleepy state.
I will post again if the issue reappears. Thanks to all for your input.
But if the answer suddenly pops into your head, please post.

Some windows updates will turn on fast boot again and I don't believe there is any notification so if you do a major update, verify that fastboot is still off.

I nuked my dual boot, and recreated it, after making sure that "fast boot" was disabled in Windows, and same problem again.
But I found this thread that mentions the issue. Apparently, any dual boot setup might cause Windows to do this.

https://forums.windowssecrets.com/sh...docs-Read-Only