You know in FontLab 7, floating coordinates of nodes are allowed. Floating coordinates help to preserve glyph shapes when you scale or rotate contours or elements. There is a set of commands in FontLab menu Contour > Coordinates to deal with floating coordinates:

1. Preview Rounding virtually rounds floating coordinates to integers and shows rounded values. This is only the view option. Actual values may be floating. If it is off, FontLab shows the actual node coordinates.

2. Round When Editing rounds floating coordinates to integers while you are editing contours. If it is off any contour edits will rather end up with floating coordinates.

3. Apply Rounding is a command which immediately rounds floating coordinates to integers. Use it to instantly round all node coordinates in a glyph.

When the Quick Measurement shows you the floating value of stem width (Preview Rounding is off) and it doesn't change when you move the mouse this means there are fractional node coordinates:

Use Contour > Coordinates > Apply Rounding to round coordinates to integers. 

When the Quick Measurement shows you the floating value of stem width and it changes when you move the mouse this means one of the stem sides is not vertical. The node coordinates may be integer in this case but they are just different:

In this case check and correct node coordinates. You may need to move a node only by one unit sometimes.