That's because Noto Sans Telugu (the font dropflow automatically downloaded based on the text; doesn't seem like a great pick but not wrong?) is returning ligatures. Not all fonts will be able to support styling individual characters. I get the same results in the dropflow playground as I get in Firefox and Chrome [1]. Maybe you were using different fonts in those browsers?
You might be able to turn OpenType features off in those browsers to make it look like your manual coloring, I'm not sure.
> if you stick with the inherent vowel on a conjunct, here making it LETTER KA, SIGN VIRAMA, LETTER RA, ditching the VOWEL SIGN I, then essentially the K from KA and the A from RA will be coloured LETTER KA, and the R from LETTER RA will be coloured SIGN VIRAMA. I haven’t decided yet if that’s an improvement!
Maybe because it changes the shaping results? I don't know enough about the writing system to understand this yet :)
You might be able to turn OpenType features off in those browsers to make it look like your manual coloring, I'm not sure.
> if you stick with the inherent vowel on a conjunct, here making it LETTER KA, SIGN VIRAMA, LETTER RA, ditching the VOWEL SIGN I, then essentially the K from KA and the A from RA will be coloured LETTER KA, and the R from LETTER RA will be coloured SIGN VIRAMA. I haven’t decided yet if that’s an improvement!
Maybe because it changes the shaping results? I don't know enough about the writing system to understand this yet :)
[1] https://jsfiddle.net/fz15xu20/