I have been having this problem for many years, but always knew a way around this (mainly by manually going through all the tables and changing styles) but I now I am sick of it and I want to know what I do wrong.
I have defined a custom table layout/style, based on the default table. However, when I try to apply these styles to a table some things do not change, or are changed to a wrong value.
Let's say for instance that I have defined that there should be no top or bottom margin on any row (even, uneven, first or last). As a precaution I also set those margins to zero for columns. However, for some reason the table still applies a bottom margin to all rows (12 pt). I have seen this behaviour before, going from a wrong background colour, to a wrong font. I don't think it's an error of Word, but I am probably something missing.
If I were to guess, I'd say that there is some kind of prioritising: the value that I have given in my style, is overwritten by something else. But by what, and how do I overrule that?