This thread has some great detective work! Many thanks to everyone who helped find and fix this.
I just downloaded and installed DFHack for the first time because my current fortress is getting old and I want to eventually rely on native-born dwarves as well as war animals and a meat industry. I ran the script, unpaused, and then something unexpected happened: My rivers thawed for the first time after playing for eight years. I'm wondering if anyone else has encountered this.
My thought - since this is supposed to be a temperate biome, and I was expecting to get freezing and thawing when I first embarked, and it rains in the spring and summer - is that the same bug that prevents critters from growing also prevents other periodic checks from succeeding, and that seasonal thawing of rivers and murky pools is one of these checks. I'm not really sure how plausible that is, but it's hard to believe the sudden thaw is a coincidence.
A more probable cause is that you had temperature off and turned it on... But if it is due to a bug similar/related to this one, it would probably be something that only affects a few % of cases, instead of the (exactly) 90% that the growth bug unaffected. The growth bug was undetected because there's no direct way to see actual size in-game*, this seems like it would be fairly obvious. Or are rivers/ponds that thaw out/only freeze once every several years more common than I thought? If so, how can we be sure a barely temperate zone like yours that only thaws out once every X years isn't intended behaviour rather than a bug.
* theoretical method to observe size in-game #1: see what dwarves can equip what weapons: bugged to always check dwarven species average size
theoretical method to observe size in-game #2: see what dwarves can equip which weapons 1-handed: mauls etc. can't be equipped at all due to bug in #1. Longswords and the regular weapons could serve as diagnostics, but militias are usually based off migrants, since not many people play for 12+ years.
theoretical method #3: pressure plate size limits. Either bugged like #1(?), or see #2 about fortress inhabitants usually being mostly first-generation. And I guess citizen-triggered pressure plates aren't that common, or they're set to trigger off even small children anyway.
method #4: indirect observation that fortress-born fare worse in combat. Aroused enough suspicion to encourage use of dfhack to check size. SUCCESS! (did I leave anything out?)