If you double-click a word in the editbox of a channnel/@window or in the scripts editor, this word (and consecutive spaces) is selected. However, if the word ends in a '-char, mIRC will select the '-char (and consecutive spaces) only.

To test/reproduce:
mIRC selects the '-char...even if you clicked a preceeding letter of the word. (It's even more puzzling for consecutive ''''')

I'm aware this is no question of "right" or "wrong"; different apps may have a differing click-select behaviour. Many browsers for example will treat a trailing '-char as "discrete", and a '-char within a word as a "separator". But I didn't see the depicted behaviour in any other app as yet. And the whole word (including the '-char) is selected if you click in a dialog edit (options dialog/custom dialogs).
Is this by design, or a minor bug?

Confirmed, that's unintuitive behaviour indeed.

Don't know if it's a bug but this is an old behavior, it probably always worked this way