I believe this is a bug. Here is the scenario:

You import a multi-layer SVG, or just create two or more layers in the sketcher.
You align the layers (ie: center relative to each other) then select them all
You can now move the group as one with the mouse click and drag method,
and all the grouped layers move as one, keeping their relative positions intact

Problem:

You want to move the group over a known, fixed distance, so you manually enter
a value in the workflow dialog box to the right instead of doing the click-n-drag.
As soon as you enter a specified amount, the alignment of the layers gets destroyed.

An easy example:
In layer 1, go into sketcher and create an object, like a circle.
Create a second layer, and in that layer, use sketcher to create a rectangle.
Select both and align so they are centered (both horiz and vert).
With both selected, you can move them around with click-n-drag.
Go over and manually move them by typing in a number or using the +/-
buttons on either axis. Result is the two layers are no longer aligned,
and it seems to send them all to a top left alignment instead of keeping
their original relative position(s).