Hello,

I don't think this is something that can be fixed but it has been
driving me crazy so I thought I'd email to point it out in case
anybody else runs into it.  If you have org-pretty-entities set to t,
org-mode does a lovely job of showing all kinds of characters.
However, the regexp for the font-locking for this makes sense for when
adding text to the end of a buffer or with point immediately before
any :alnum: character (e.g. not a space).  It makes less sense if you
start inserting some text in the middle of a sentence, say, which I do
often when writing papers...

See attached image for an example.  If you have something like "some
text", place point after the first "e" and start typing "\left", as
soon as you type the "e", you will get the \le symbol despite typing
the "f" immediately after.  The regexp for font-locking is fine for
converting text that has already been typed; it is less effective when
inserting the text.

If, instead, point were at the first "t" in "some text", there's no
problem inserting "\left".

Unfortunately, I cannot suggest a fix.  It's not that serious a
problem; I just wanted to highlight it for the mailing list.

In the image, you'll also see that there are some problems with
underlined text when org-hide-emphasis-markers is set to t.  Again,
not a serious problem (and underlining is really a hold-over from
typewriter days, as I believe Carsten would say... ;-).

Back to writing... ;-)