I've never heard of weight training (or anything for that matter) affecting height. The only thing I can think of is maybe your feet have swelled after working out, making you ever so slightly taller?
Or maybe your posture in the morning is different than your posture in the evening.
Hey! None of these numbers need to have that much precision. Half an inch isn't going to make or break things. BMI is only a rough guideline anyway, and it's a range of values.
I'm thinking maybe your spine/discs compress during the day? You could try incorporating Pilates and/or yoga into your w/o routine. It helps strengthen and lengthen the spine. Look into it, might help keep things on an even keel.
The variations in height between morning and evening has to do with the vertebral discs. In the morning, as you have been resting all night, the discs are not so flat as in the evening, so you may have a difference of 1, 2 cms. As far as I know, heavy weight training does not affect height.
Bye