A string containing a leading Unicode nonbreaking space (\u00A0) did not have that character removed by [string trim ...] (no chars specified for removal).
In Unicode there are several "whitespace" characters that [string trim] does not remove by default. (See http://en.wikipedia.org/wiki/Whitespace_%28computer_science%29
for a working definition of white space.)
Ironically, [string is space ...] will return 1 for most of these characters, signifying that at some level these characters are known to be spaces.
Interestingly, the Unicode NEL (Next Line), \u0085 gets 0 from [string is space \u0085].
So do the following two:
U180E MONGOLIAN VOWEL SEPARATOR
U205F MEDIUM MATHEMATICAL SPACE
There are 3 issues then.
[string is space ...] returns the wrong results for certain Unicode characters.
[string trim ...] (the form without characters specified) is not deleting Unicode space characters.
The documentation for [string trim ...] is not precise about which space characters are deleted (or not deleted).
The behavior of [string trim ...] should (in my opinion) be defining as removing those characters for which [string is space .] is 1.
If [string trim ...] only trims ASCII white space characters, then they should be explicitly described and listed.