Fill brush does not always fill properly

I have looked around on the forum, generally via a search engine and also via very specific search operations via a search engine targeting the forum as search area, but found no answer to my question. In any case, I suspect it is a fairly simple matter to be addressed.

In using version 2.75a I’ve often gotten the case that the Fill brush operation to quickly texture selected faces does not always fill said faces. Often there are (black) holes or spots left that need to be filled up.

I really need a solution to this, as the current project I’m working on requires the proper feature a lot. Using workarounds would consume way too much time, I reckon.