phpThumbOf cache not cleaned

[oo12]

phpThumbOf's cache is never cleaned according to the settings in Core > phpThumb. This happens because the cacheClean() method calls CleanUpCacheDirectory() from the phpThumb class in the MODX core, but this method only deletes files beginning with the string phpThumb_cache_ (here's the relevant line), which is rarely if ever the case for cached images generated by phpThumbOf.
So calling cacheClean()—and it's called every time phpThumbOf is run, whether or not the thumbnail is cached—simply takes up time scanning the cache without producing a result. On sites which have a large number of images in the phpThumbOf cache this creates a noticeable performance drag, especially when there are multiple images on a page.