To make your buttons appear immediately, you need to clear your local
browser cache.
This caching problem should be fixable. I suggest:
1. Appending your own version string onto $wgVersion, and update it every time you release. 2. Append the version string onto every JS and CSS file reference, e.g., /foo/bar/mystyles.js?v=1.9.3.local.17
DanB