Double Duration Plugin

Searching around, it seems there is no plugin to double the duration of a large group of notes. There is however a plugin for the opposite (HalfTime - http://musescore.org/en/project/halftime). I admittedly know nothing about javascript or writing plugins for musescore, but it seemed like a simple enough change to make. So, I just changed chord.tickLen/2 and rest.tickLen/2 to chord.tickLen*2 and rest.tickLen*2 and renamed the file to DoubleTime.js (btw, that naming seems backward to me). It works for the most part, but full measures of rests in the output are totally screwed up. No rests are actually visible and sometimes note entry mode behaves like that measure doesn't have as many beats as it should. What's going on here? .js (changed to .txt) and .mscz attached.