Just checking this isn't known about before raising a bug report.
stem-length-estimation.ly is described as "Stems with overridden 'length
should not confuse height estimation. This example should fit snugly on one
page.". That'll be 1 1/2 pages in 2.13.40. Running it against 2.12.3 gives
an error because of the new spacing names, but actually takes 2 full pages.