Huh... Baseline grid alright... My mistake, thxs for spotting it.
Justify vertically a text that is aligned on baseline grid has that effect : 1st and last lines are aligned while the others act as non aligned. So in this specific case, it would do the trick. Now, extra space is just normal behavior and I wouldn't care either, just like Barbara.
About modifying the text, it also could be a solution, but what if you do loads of modifications and then have to do The One that would reflow everything? Urgh... I wouldn't go that way personally...
I micro-manage so many page elements—this is one that just doesn't bother me at all, and it's because overall the columns are even—texts starts at the top margin and ends at the bottom margin. Even my pickiest clients would let this go.
And, Viinny, I agree with you that it's the Keep with Next setting on the body text, that impacting the left page.