Perhaps FBReader doesn't understand EPUB3. This is the correct way to set Series metadata in EPUB3:
Code:
<meta property="belongs-to-collection" id="id-3">TestSeries</meta>
<meta refines="#id-3" property="collection-type">series</meta>
<meta refines="#id-3" property="group-position">124.0</meta>
This is the correct way for EPUB2:
Code:
<meta name="calibre:series" content="TestSeries"/>
<meta name="calibre:series_index" content="124.0"/>
I don't know anything about the "1.2e+02" problem, though.
Make sure you haven't enabled "Upgrade book internals" in Polish.