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Untitled files are stored in iCloud if iCloud is enabled. Please check if you have untitled files in your iCloud and delete them if you do not need them anymore. This will reset the counter.
I'll try to reproduce it with the app you mentioned. Is it this one? https://itunes.apple.com/de/app/mega/id706857885?mt=8
Hello,

the Inbox folder is created when you use "Open In" to open a file from another app in Textastic. Unfortunately, in recent iOS versions, once created by the system, this folder can't be deleted by the user. I'll consider hiding this folder in future releases of the app.

Textastic moves files from the Inbox folder to the root folder and tries to delete the Inbox folder (which fails since iOS 7). In earlier iOS versions, the user wouldn't see the Inbox folder at all.

I haven't seen the Cocoa error 513 issue before. On my iPad I can edit files that were imported with "Open In" (and are now in the root folder) just fine. I just confirmed this by opening an HTML file from the Dropbox app in Textastic and editing it. Which iOS version are you using?

I don't plan to change the icon at the moment, sorry.
It's great to hear that it works now!
vSSH seems to be an SSH terminal client. If you can connect with it it doesn't necessarily mean that SFTP is enabled.

The Synology SSH server has SFTP disabled by default. You can enable it in DSM.

What do you see when you are in DSM and go to Control Panel -> File Services -> FTP -> SFTP?

Here's a screenshot of how that looks for me on DSM 5.0:

Does your SSH server have SFTP enabled? The SSH authentication, but then the operation times out.

Can you have a look at the server's log file?
In the current version, a crash happens when an HTML file references other files (like CSS or JavaScript) that are not yet downloaded from iCloud. Make sure that you open all directories with the files that are referenced by the HTML file. This will trigger a download from iCloud.

I'll fix this in an update.