When choosing Crop tool there is a padlock symbol that shows whether aspect ratio is locked or not. When making the first attempt to crop any particular image the padlock symbol incorrectly shows as unlocked when the tool is behaving as locked.
This only seems to happen on the first attempt to crop a new image.
Whilst the symbol incorrectly shows as unlocked (even though aspect ratio is locked), just passing the mouse pointer over the padlock (no click required) changes the padlock to correctly show as locked.
Whilst incorrectly showing as unlocked (even though aspect ratio is locked), pressing the shortcut key A has no effect on the padlock symbol but does change the aspect lock to unlocked (so now the symbol and the behaviour matches). Subsequent use of the shortcut A makes padlock symbol behave correctly for that image.
Once the initial incorrect view has been corrected (by one of the above methods), all subsequent behaviour on the same image seems correct. Open another new image and the problem reappears.