It is definitely not nice. I can explain why the problem happens, and then you can decide whether it is a feature or a bug, and perhaps who is to blame
The problem comes from Windows font edge smoothing (ClearType). Font smoothing is done by blurring the pixels a little into the surroundings. The eye/brain percieve (is that the right word?) this as more smooth.
The blurring means that each letter is actually using one pixel more in all directions. Writing several letters at once with one of the writing routines will not cause any problems because the overlap between the letters will be handled by the write operation. But if you write some letters with one operation and then some more with another operation then the last write will reset some pixels in from the first operation in the overlap.
And that is what happens to your comma, it is effectively erased by the next letter (there are most likely some not fully colored pixels left from the comma).
The editor use many write operations to do the token coloring, because a single write operation will use same font, color, etc.
There are means to solve the problem, but not in existing programs. The next (7.4) IDE will use the Scintilla editor which have solved the problem.