[texworks] Plane 1 characters not visible in TeXworks

[David J. Perry]

Hi everybody --

I'm creating a test file using, among other things, the Old Italic 
characters of Unicode (U+10300 etc.).  I copy and paste the characters 
from elsewhere into TeXworks, but they are not visible. If I run the 
cursor over the line, the right number of letters seem to be there, and 
they show up correctly in the PDF after the file is typeset.  I can copy 
the text from TeXworks into another app and the OI characters appear 
just fine.  So they are there, just invisible.

I have tried two different fonts for editing in TeXworks, both of which 
I know for certain contain the OI characters.  Any ideas why they are 
invisible?

David