You seem to have Edit>Preferences>General>Use Preview Bounds ticked.
You should not find the change of numbers without a stroke.
nope, Use Preview Bounds is not ticked.
There's also no stroke applied to the rectangle.
I am also able to reproduce the same at my end.
You seem to have selected the option for "Align New Objects to Pixel Grid" while creating a new document under the "Advanced" label.
To check this you can open the Transform panel from Window menu and check whether "Align to Pixel Grid" check box is selected or not.
Deselecting this checkbox solves the problem at my end.
I believe MBM has it: 8.114 is 23 px.
This would mean that unless two sides are at whole pixel numbers, the rectangle moves a bit as well.
Hooray! Thank you MBMSumraat! "Problem" solved.
I have no idea when and how I've activated this option …
The option 'Align to Pixel Grid' is by default ON for 'Web' and 'Flash Catalyst' Document profiles. Please see if you are using any of these profiles for your new documents.
Ah, ok - that's it - thanks!
As mentioned correctly by Jacob, since 8 mm is quivalent to 22.6768 px, so when Align to Pixel Grid is ON for a document which is ON by default in case of Web and Flash Catalyst, it rounds it up to the next whole pixel number so that the object can pixel aligned.
You should change your Document profile if you are not designing for web or flash rather than unchecking that option. There are other settings in some of the Document profiles specific for print vs web. It could save you other headaches down the line. Illustrator will default to the last Doc Profile you used so picking the correct one should be a one time thing unless your work has you designing for different mediums.