I suppose my main problem is that it actually
does preserve some settings, but not all. I'll try to explain my reasoning a bit further and hopefully clearer.
I draw a shape using

. I give the stroke of this object a red colour, 0.7 mm width and round joins and caps.
I turn off the stroke paint and leave the object alone for an indefinite amount of time.
I go back and turn the stroke paint on again.
The object will now show a stroke with a red colour, 0.7 mm width and round joins and caps.
This tells me that turning the stroke paint off doesn't erase the properties of the stroke, it just hides the stroke alltogether.
Now I select the object and turn the stroke paint off.
With the object still selected, in the preferences for

under "Create new objects with:" I select "This tool's own style" and hit the "Take from selection" button.
I proceed to draw a new shape using

.
I select my newly drawn shape and turn the stroke paint on.
The object will now show a stroke with a red colour, 0.7 mm width and miter joins and butt caps.
This is what confuses me. The colour and the stroke width are preserved, but the join and cap shapes aren't. If I copy the style of an object for my new shapes, then I expect the newly drawn objects to have the exact same properties as my copied style. If I turn the stroke paint on for both objects, I expect them to look the same (or at the least for
all settings to be defaulted, not just some).
I did some quick testing, and I came up with this set of changes (or lack of changes) for when this procedure is done:
Colour: Same as previous object
Stroke width: Same as previous objects
Width unit: Same as previous objects
Join shape: Reset to Miter join
Miter limit: Reset to 4.00
Cap shape: Reset to Butt cap
Dash pattern and marker: Reset to none
I suppose using a preset style would help with this particular problem, but I had a good reason to want to use the "Last used style" (I just don't remember what it was right now...).