[QScintilla] Editor with a custom lexer keeps flashing when editing

[agarny at hellix.com]

>> Is the Qt update the only change? Can be behaviour be reproduced in a
>> simple, self-contained example?
> 
> The only thing that is different is indeed the fact that I have
> upgraded Qt from version 5.4.2 to version 5.5.1. Everything else is
> the same, i.e. same version of OS X (10.11.5) and Xcode (7.3.1).
> 
> I am going to see whether I can come up with a simple, self-contained 
> example.

Ok, I have just modified your example (so that it now makes use of my 
lexer) and I can confirm that the 'problem' I reported is indeed present 
(the code can be downloaded from 
https://www.dropbox.com/s/jhvrifo23vn72qv/example-Qt4Qt5.zip).

Once you have built and started your example, simply paste the following 
code:

---------------------------------------
def model my_model as
enddef;
---------------------------------------

 From there, just try to edit the first line and you should see that line 
flashing repeatedly. With my 'fix', the problem disappears, but is it a 
good fix?...

Alan