Well, the issue is not as clear as the preceding answer states.
One issue here is morpheme-boundary.
It's not good policy to look for minimal pairs that involve morpheme boundaries. For example, drink drank drunk is ok because there is no boundary involved here, but there is the well-known case of Scottish English where vowel length normally does not exist, but some long vowels actually exist in words like Preterite laid < lay+ed. In other words, your pair wugi / wuga is not a fully satisfactory minimal pair. It might involve interferences caused by morpheme boundaries. So I would recommend to look for another minimal pair that does not involve that kind of issues.