Courant number dependant on case file
 

Hi,
I've encountered a strange problem. Am running a CHT transient 2D problem. Started with a TS of 1e-5, after a while checked te courant number, it was about 4. So I wrote a date file, increased the TS to 5e-5, wrote a case file and restarted.
NOW, when i opened the previously written data file with the new case file it shows a courant number of 20 !!
So basically when i open the same data file with 2 different case files (the diff being the TS) i get different values of Courant numbers.
What have i done wrong??

Regards
Luke