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://wordpress.org/plugins/wp-latex/