I wonder if it might be appropriate for the precedence table to mention this unexpected (by me) interaction?
No, I don't think so. The ':' isn't an operator, so it has nothing to do with precedence. It doesn't belong in a precedence table. Determining whether something is an operator (or part of an operator) or not isn't dealt with with the operator precedence table.
Since the word ‘attribute’ does not occur in perlop or perlsyn, and since no other punctuation mark requires a visit to perlfunc to figure out how it parses
But you only find something about attributes in perlfunc because my was specially added to perlfunc; my isn't a function. The details are in perlsub, where you would also go for punctuation as prototypes and some cases of parenthesis.
Is there any unified list of officially undefined things?
Not that I know of. But by all means, feel free to write up a list and submit is as a patch. Writing documentation doesn't require any coding language, which means most people can do it.

In reply to Re^3: Unexpected parsing by JavaFan
in thread Unexpected parsing by JadeNB

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