Hi Michael, many thanks for your kind reply and explanation, I am very grateful.

Yes, I did notice the vcenter, flex and hbox tags. So, I'm guessing that the vcenter tags would need to be within the flex tags for it to work correctly?

Yes, I did consider that there might be an element of the command bar that is taller than the rest. Is there a way that I could troubleshoot which part is the one that is potentially causing the issue? I suspect that it may be the custom UI scripted parts, specifically object library, scripts and lighting? As you may have noticed, I did try to remove the text from the icons and I'm not sure if I did it correctly, so that might be causing an issue too? I'm wondering if despite removing the text, it has left the empty space where the text would be and thus thrown it out of alignment?

Thanks again for your time and insight.

Tim