How does changing 'Dimensions' fields at once exactly work? For related X, Y, Z fields of Location, Rotation  and Scale in the Transform panel of the 3D view 'N-Region', there is a possibility to change the 3 fields at once. It can be done with the mouse or with numerical input.

  

But it seems 'Dimensions' fields behave strangely (entering individual values works as expected). Sometimes the value is lost after being entered, sometimes only two fields are changed. An example:

  


When using the mouse, Y is left unchanged (expected: All values adjusted in proportion).
The final dimensions X and Z are different (expected: Final values are starting values times the same factor).
When entering the value 5, the result is 2 (expected: 5, whatever the scale value).


Is this a bug?
If not, what is the reason to prevent this single input?

Using 2.79b.
It is not a bug, it is a well known limitation of the current system, as you can see in the bug repot.


  Object dimensions are broken and an abuse of RNA, IMHO - the same
  problem happens from Python and we had it reported too.
  
  Basically they rely on one axis being set, then updating - before the
  other values are set.