Saving causes indents in to change

I try to always work in code view and save every minute or so, out of habit.

Anyway, when I save the line beneath where my cursor is changes so my code then become jagged and untidy. If go back and tab this line in and save again, the line beneath jumps to the left and when I tab that line in and save the line beneath does  the same, regardless of whether it is a tr, td or th.

I am using a table format as I am displaying things that work well with a table format.

I am using a Mac (updated to ver. 10.12.6) and Dreamweaver CS6.

Any help gratefully appreciated!

Thanks in advance!