When I select a // comment and use the spell check tool bar I'll always get a "Spell check complete" message even there is a typo.
When I select nothing (I assume that in this case the entire file will be checked) then the spell checker finds the typo.
Info: The typo is in the very first line within a comment:
// first line with a typo sdfkjas+?dfkl
// second line without typo
// third line without a typo
Found in current release (10.6) downloaded today from Whole Tomato Software home page.