The problem is that I do not save the file as .txt by myself. When trying to save changes, Textastic puts the message into the log-file. I don't even want to use a .txt extension in this certain use-case so I don't know where it is coming from.

I tried this on two user-accounts, one had iCloud enabled - the other one had iCloud disabled. The problem occurred in both cases.

Video: No problem ;)

http://www.ipernity.com/doc/275771/14550035

Both questions: no. But I've found something interesting:

Filename "test" -> no problems,

Filename "test.html" -> causes permission denied error.

Edit:

The Console-Log says:

24.03.13 15:24:38,755 Textastic[12262]: -[NSFileCoordinator itemAtURL:willMoveToURL:] could not get a sandbox extension. oldURL: file://localhost/Users/username/Desktop/test.html, newURL: file://localhost/Users/username/Desktop/test.txt

The same Mac OS X version over here, 10.8.3 ML.