Now this is something I didn't expect to encounter - when subways states that their meats in the store are halaal, that is precisely what they mean - the stuff on them might not be.
Someone at work mentioned that Subways Chicken Teriyaki ay not be halaal due to the addition of alcohol. A quick google search leads to this webpage with an email from subways that contains the following:
In response to your specific enquiry about the Teriyaki glazing: there is indeed a small dose of Sake used during the production. However, the product was approved for consumption at our Halal locations because the cooking process reduced the alcohol content to a negligible level. Nonetheless, we are in the process of testing a new recipe for Teriyaki chicken that will eliminate the use of alcohol in the process.
Now I did not expect this - Subways had gone out of their ways to prevent non halaal meats, but not extending this to the whole product is really bad IMO.