I was recently reminded (by this question) that intervocalic single -s- turned into -r- by rhotacism, and later new instances of intervocalic -s- were produced from -ss-. If the vowel preceding -ss- is short, then the transition -ss->-s- transforms the syllable from long to short (heavy to light). This is significant especially for metric poetry. I would expect this shortening to be compensated by elongating the preceding vowel. Although many -s- are preceded by a long vowel, there some examples of a short vowel followed by a single -s-: posui, casa, asinus.
Are there any examples where compensation is known to have happened? Or is the intervocalic transition -ss->-s- something that was allowed to freely change syllable length (weight)? Are the words I listed (and others like them) somehow exceptional while most words did have compensation?