"z" key misbehaving in Vintage insert mode

When I enable Vintage and enter insert mode, I am unable to type two consecutive z's. The second z is causing Sublime to replace the previous letter. So, for example, if I type "pizza", I will get "pia". However, type "size" has the expected result. Disabling Vintage alleviates the problem, but then I lose all my wonderful Vi shortcuts, which makes me very sad :(