Slayda, as explained above, absolutely everything is 100% consistent, with a
single exception:
paragraph spacing, which gets reset to the publisher default upon opening a new book.
I believe we are misunderstanding each other here.

Because there are really
2 meanings of the word "consistency". As an example formatting feature, let's take
font size. There are 2 possible meanings as to what it means for Marvin to be "consistent" regarding font sizes:
- When opening a new book, initially display the same size compared to the publisher default as in the previous book. If the fonts are enlarged by 10% in book A, also enlarge them by 10% in book B.
- When opening a new book, initially display always the same size of the main text, completely disregarding the code in the e-book.
Right now, Marvin is using approach #1. What you, Wyndham, and perhaps other Marvin users seem to be expecting, is approach #2. Such as, telling Marvin that you would prefer your main reading font to be
always 12 pixels, and that Marvin should always
initially open and display a book using
that main font size.
I have no idea whether displaying e-books in this way, using approach #2, is technically possible; that is up to Kris to answer. One problem may lie in determining what
is the book's "main reading font". Sometimes, there is a Preface in a book, or some lengthy technical notes, blurbs and whatnot... These can appear in a different font size from the rest of the book... what then? How is Marvin supposed to "guess" which font in the book it is that you wish to see displayed sized 12 pixels? Or, would you simply "level" all fonts in the book to the same size, so that blurbs, endnotes, main text, etc. etc., would all display in the same font size? Would such forcible uniformity of font sizes, disrespecting the original book, really be desirable?
The same dilemma, as explained above pertaining to font sizes, also applies to line spacing and paragraph spacing. Margins are 100% consistent in Marvin even today.