This is more noticeable with wide or tall images like this one.
In this case, the resolution 1518x500 which gives a 1:0.32938076416 ratio
Here’s the example of applying this ratio via the pos/rot/scale menu which is the proper size:
And here’s the example of applying this ratio via the Object Scale menu which is the incorrect size:
For me this creates the problem when I’m resizing a lot of things, some that need a unlocked scale, and some that need a locked scale. When going to a locked scaled item to an unlocked scaled item and adjusting it (or sometimes not doing anything), it resets it to be locked scale, making me lose the proper scale of the item. This is entirely avoidable when doing the same thing but with the Object Scale settings as nothing can automatically change that.