Hidden Characters

I have to following code that does not parse:
$$T_{aussen} \approx 273^\circ K + 25^\circ C \approx 300^\circ K$$

The “same” code does parse:
$$T_{aussen} \approx 273^\circ K + 25^\circ C \approx 300^\circ K$$

The problem seems to be hidden characters. If you look at the url sent to the server you see a difference:
http://s.wordpress.com/latex.php?latex=%20T_%7Baussen%7D%20%5Capprox%80%84273%5E%5Ccirc%20K%20%2B%2025%5E%5Ccirc%20C%20%5Capprox%20300%5E%5Ccirc%20K%20&bg=T&fg=000000&s=0
http://s.wordpress.com/latex.php?latex=%20T_%7Baussen%7D%20%5Capprox%20273%5E%5Ccirc%20K%20%2B%2025%5E%5Ccirc%20C%20%5Capprox%20300%5E%5Ccirc%20K%20&bg=T&fg=000000&s=0

%80%84 are the bad once. Other characters producing the same problem are %E2 and %C2.

I don’t know how to handle this. Some times the characters get added by simply copying the code from one place in the text to an other.

Any ideas?

Thanks!!!

Lukas

https://ww.wp.xz.cn/plugins/wp-latex/