Potentially related to: #1782

Can't find an official specification, but many explanations of the Newick format mention space in identifiers is invalid:

The whole line is loaded as one unit, so no white spaces or tabs are allowed in any of the identifiers or numbers or before or after parentheses, kommas or colons.

Source: http://bioinformatics.intec.ugent.be/MotifSuite/treeformat.php

Tips are represented by their names. A name can be any string of printable characters except blanks, colons, semicolons, parentheses, and square brackets.
Because you may want to include a blank in a name, it is assumed that an underscore character ("_") stands for a blank; any of these in a name will be converted to a blank when it is read in. Any name may also be empty: a tree like
Blanks can be inserted at any point except in the middle of a species name or a branch length.

Source: https://evolution.genetics.washington.edu/phylip/newicktree.html

Scikit bio's formal grammar shows that whitespace is invalid, so scikit-bio will error, as I would expect Bio.Phylo to do as well.

The issue is that the current regex expression that matches an unquoted label returns several tokens for an invalid unquoted label string:

Therefore, _parse_tree iterates over the four different unquoted label tokens and updates the node's name four times in a row. So, the final node's name ends up being the last token in the regex group above. That is why your label ends up being whitespace and the function does not throw and exception.

The solution I have come up with is to return the entire unquoted label string with whitespaces, carriage returns, etc. included, and do the checking manually when the _parse_tree method encounters an unquoted label token.

The following changes should do the trick:

# NewickIO.py

UNSAFE_CHARS = ['\r', '\n', '\t', '\f', '\v', ' ']
tokens = [
    (r"[^\(\)\[\]\'\:\;\,]+", "unquoted node label"),
]

# ...

def _parse_tree(self, text):
    # ...
    for match in tokens:
        # ...
        else:
            # unquoted node label
            token_has_unsafe_char = any([c in UNSAFE_CHARS for c in token])
            if token_has_unsafe_char:
                raise NewickError(f"Invalid character detected in node label '{token}'")
            current_clade.name = token