I can confirm, that TCL displays the same character as Idle, hence it 
itsn't a bug in Python (cf. the screenshot).
Unfortunately, I couldn't identify the font used here; I'm not able to 
modify and recompile Tk, as suggested, but I tried to check the 
possible serif fonts visually.
None of the fonts listed in Word is identical to the one used for 
capital sharp s in tcl (I created a simple app with Tkinter Label-s 
showing the pairs of the characters in question using the potentially 
similar fonts; while some are really close, in all cases there are 
various differences in glyphs; )

In any case, I guess this isn't a problem in python, which would have 
to be further examined; I have quite a lot of fonts installed, probably 
with some of them behaving in some "non-standard" ways