Makes good sense to me, and just un-ticking maintain aspect works. One thought I had was a potential 'forced aspect' selection mode where only selections that exactly match the given ratio are offered.
Your explanation set off a rube goldberg machine in my head, too. Far beyond the scope of a bugfix. But I thought I'd share it.
The undo data contains a list of previous commands, doesn't it? If so, most of the information needed to make context-sensitive decisions is already there. But for most users, having a command do something different (if only slightly) based on when and where an action happens would be very frustrating. So what if there were a way, in some deeply buried menu, for advanced users to overload existing commands or define their own code. And a way to configure the heuristics as well.
In my example: Command 1- fixed crop, Command 2-resize
If these two commands are run in succession, run Magical-Handwavy-Function to check and force dimensions to 1200x900
No need to reply if I'm off my rocker. I need sleep!