Unfortunately some older fonts have some problems with S-comma below and T-comma below characters, comma is not below the S and T letter, is part of the letter. This happens also on Windows 7.
The two characters are part of Unicode's "Latin Extended-B":
I have done a simple test, to see how many fonts (from the Latin Windows fonts) have the S and T comma below characters with actual comma below symbol.
The simple test consists in a webpage rendered Internet Explorer 8 and 9 on Windows 7 with normal font size (96dpi) and with large font size (120dpi).
The test includes besides the Romanian characters (ĂÂÎȘȚăâîșț) also the "deprecated" S and T cedilla characters (ŞŢşţ) and S and T dot below characters (ṢṬṣṭ).
Test pages and screenshots for Internet Explorer 8, 9 and Firefox 5 can be found here. The results for 96dpi are presented below:
"Tahoma", "Segoe UI" and "Microsoft Sans Serif" have S and T dot below characters which have the dot separated for the 9pt and 8pt font sizes, which is not true for S and T comma below characters.
The same test pages on Windows 7 with large fonts (120dpi) displayed correctly the comma for all fonts (except Franklin Gothic Medium).
Internet Explorer 9 comes with a new font renderer (using DirectWrite and Direct2D APIs) which reveals another problem with the S and T comma below characters. The comma below from S is different from the one under T, as seen in the images below:
S and T cedilla characters, even tough not correct from the Romanian language point of view, are still heavily used in many documents / web pages etc. It is important that the cedilla should be drawn the same for S and T. This is not true for all Windows 7 fonts.
Firefox starting with version 4 includes locale dependent text rendering, which means that if you have the Romanian locale set the S and T cedilla characters will be automatically rendered with S and T comma below characters. Not all the Windows 7 fonts come with this locale information. Read more about this feature on Wikipedia.
The results for S and T cedilla are illustrated below: