I confirm that
- selecting "spell check while typing" or
- unchecking "intelligent" quotes in System Prefs -> Text
both make my problem disappear. You might also want to check the options in Mail->Edit->Substitutions->Show substitutions menu: maybe the "Curvy quotes" checkbox interferes with the global setup in the System Preferences...
However my problem was sligthly different: whenever entering an apostrophe (') at the end of a line (i.e. ALWAYS when normally typing new text before a signature!!!), the cursor jumps to the next line, so that it is impossible for me to write
we're
When I type that, I get
we'
re
instead.
More generally, when I try to insert an apostrophe inside a word, the cursor jumps after the next letter. So typing
abcde
and inserting apostrophes after the first letter a (by going back 4 chars, or setting cursor with the mouse), I get:
a’b’c’d’e’
‹›’’’’'
instead of the expected
a''''''''''bcde
(I selected the "intelligent" quotes to transform 'single quotes' into ‹single quotes›, so that the transformation can be seen)
In this example, inserting the quote after "e" at the end of line makes the cursor jump over the next character (i.e. newline). Then the next apostrophe at the beginning of line is immediately transformed into an opening single quote . The next one is transformed into a closing single quote. And the following ones are undecided/untransformed.
To get even more fun: after the previous example, try moving 4 chars backwards, and press fgh You should get:
a’b’c’d’e’
‹›’f’’’’
gh
Now it's standard characters that make the cursor jump over the apostrophes!!!
It thus seems to me that the "intelligent quote" algorithm going on when a quote is pressed has a completely flawed "look-ahead+memory" mechanism. It might be confused by the content-encoding of the rich-text format: some have more bytes-per-chars than others... And by the way, where has gone the content-encoding selection of rich-text messages???