Doubt regarding IME

Hi All,
 
I'm facing a strange problem with IME. 
 
Here goes the scenario. I've written the string 8890 in a text file (.txt) and saved it. Now I've opened the file and open the search dialogue box. At this point I've used the IME and changed the language option to Japanese (Hiragana). Using IME I typed 8890 and try to search the string. The string was not found. However, if I write the same string in the text file using the IME, the string can be searched in the  above described way.
 
Please let me know what is the reason behind this observation. Does IME use completely different types of encoding for different languages even for the numerals ?
 
Regards,
Sourav