There are almost always exceptions with English pronuncation I'm afraid. With the example you gave, I can think of some:
ate- some say 'eight' and others 'et'
Forbade- pronounced 'forbad' by many
delicate (and many others)- the 'a' is pronounced as a schwa
Try to think of them as guidelines rather than rules. English spelling and pronunciation are inconsistent because English is a mixture of languages and has different spelling systems at work.