There is generally a logic to it - perhaps not the logic you want though!
Word has always effectively stored paragraph info inside the, normally invisible, paragraph mark (with document info inside the last paragraph mark). It has to keep it somewhere linked to the text. The best way to make word more predictable is to take the time to get to grips with paragraph styles which lets you set rules about what happens when you start a new paragraph.
The way Word handles en & em dashes does have a consistency about it too. an en (short) will be turned into an em (long) dash when it has a space each side after you type the next word followed by another space or a punctuation mark
. You have to be careful if editing text not to forget that, if you want to add a word after the dash, and you want it to turn into an em dash, you need to type a space (or punctuation) after even if you immediately delete it.
Out of interest, what do you find so stupid about Excel? Maybe I've just used it for too long to notice.
Just don't get me started about Publisher!!
"If I have not seen as far as others, it is because giants were standing on my shoulders."