The Pronunciation of Vowel Sounds Can Cause a Chain Reaction

The pronunciation of vowel sounds is far from precise, even among people who speak with the same accent. A particular vowel sound can vary a little bit from one speaker to the next. There's usually a range of acceptable pronunciations of any given vowel sound. That range can vary over time. Sometimes people extend their vowel sounds into the spaces occupied by the neighboring vowels. They might pronounce a as a or a but it can also work the other way where the pronunciations vary quite a bit.