TolpuddleSartre:
Don't they all use the same front-end? :o
Improvements are made and bugs fixed/introduced with every release. If every release was identical there would be no point in making them.
In Arduino IDE 1.6.6 and newer, function prototype generation is done by a tool named arduino-builder. An IDE release will often contain a new version of arduino-builder. Arduino IDE 1.6.9 uses arduino-builder 1.3.18. Arduino IDE 1.8.5 uses arduino-builder 1.3.25.