This is a common issue when using 1-Click Book Creation or Microsoft Word (in general).
Microsoft Word uses what are called section breaks to 'segment' the document. These differ from page breaks in that the latter are used to 'force' the next item on the page to the top of the following page. However, section breaks allow you to change the structure of the page itself, i.e. from portrait to landscape (and back again), the headers and footers, and even the page number-types, i.e. lowercase Roman numerals or Arabic numbers.
The way Microsoft Word works is it links section breaks by default. It's your job as the author to unlink them if you want to do something different. So, if you have a book with lowercase Roman numeral numbering in the front matter, and you wanted Arabic numbers in the main body of your document then you would need to use a section break - this is impossible to achieve with a page break.
But, before you can do it, you need to unlink the lower section from the upper section (sections always link 'up': section 2 is always added after section 1 in the document; 3 after 2, and so on). Once you've done this, you can then insert your respective numbering types in each section.
The problem here is if you accidentally delete that section break and relink/merge those sections: most likely 1 will become the same as 2, i.e. you will lose your lowercase Roman numerals.
You need to insert a new section break, unlink the sections, and insert new numbers.
Sounds easy, no? It's a pain but I've written 2 blog posts which explain in more detail: