Open default directory

I encountered an error in one of our controllers, in which i assumed that the default directoy of the function Open is "HOME:" (as in Example 2).
But that gave me sometimes a file not found error.

So instead I'm now using the (more often seen) Open function call like in Example 1 from the documentation and everything runs fine.

In contrast to the documentation, I was reading or appending and not writing a file.
Is this an expected behavior?

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