If you look closely at your "$_sensor_type =" statement, you will see that you have different kinds of quotes around "I2600". Notice the difference between them and the first quote in your print statement, ". forward leaning and backward leaning " are different than normal straight up ".

I am surprised that this even compiles. Are you using warnings and strict?

Other than that, I see no reason why I2600 shouldn't match the regex, although the /g is completely unnecessary here. I tested "I2600" on my machine and works great with proper quote characters.

UPDATE: this is not the problem, it appears that previous use of string in an inappropriate global match was the issue..oooops. Although I must say that sometimes these non-printing and/or non-standard characters can and DO cause problems... that is not the case here..