Having not long ago consumed delicious gooseberry fool, I quite naturally got to thinking of the derivation of the word gooseberry and its rather surprising pronunciation. The OED tells us, somewhat glumly:
[Prob. f. GOOSE n. + BERRY n.
The grounds on which plants and fruits have received names associating them with animals are so commonly inexplicable, that the want of appropriateness in the meaning affords no sufficient ground for assuming that the word is an etymologizing corruption, e.g. of Du. kruisbezie, G. krausbeere, or of a hypothetical *gorseberry or *groseberry (see GROSER, GROSET); though the last derives some little support from the existence of the form GOZELL for *grosell.]
Why the word should be pronounced [ˈɡʊzb(ə)ri] remains a mystery, as does its extended meaning of “chaperon”. I understand that this is a chiefly British usage. In the USA the phrases third wheel or fifth wheel are used.
And why is the raspberry [ˈrɑ:zb(ə)ri] so called and so pronounced? Answer comes there none. OED says that the derivation is RASP + BERRY, but RASP is a now obsolete word meaning….er….a raspberry. However, there is an explanation for the extended meaning of the word raspberry (= a rude noise made with the lips). This is rhyming slang and the full version is raspberry tart.
The voiceless to voiced assimilation in these two words is not found post-lexically in English and the only other word that I can think of (at the moment) where a similar change takes place is husband.