I find this kind of discussion fascinating, because here we have a bunch of highly experienced type-rated pilots, all with a slightly different interpretation of how/why a feature works and what to do if it isn’t performing as you want. This is not a dig at any of you, but an example of how the UI and documentation of the same on many aeroplanes is far from ideal. Even between different operators there seems to be alternative ways of dealing with the situation.
Over in Boeing World, there is a very similar thing with ALT (no *) but it serves for capture and hold, with quite a few quirks for the unwary. There are phases of flight where pressing the brown button (does the same as the AB red one) is preferable to improv jazz on the MCP which may or may not have the desired result...