[WalterWalter]

When creating/importing/converting an ebook in .epub format, the metadata for the series in the bookfile for the series is something like:
<meta name="calibre:series" content="TestSeries"/>
<meta name="calibre:series_index" content="124.0"/>
when running "Polish books" this changes to
<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 has two consequences/problems:
1) Some e-book readers do not understand this. I use "Calibre Companion" to manage the books I read on my smartphone. When I open a book to read, then Calibre Companion opens the FBReader App, which does not recognize this as series information, and the book info will not contain the series information, so looking up books in FBReader library, the option: sorted by series, does not work. That is a little bit annoying but not so bad, since I decide within Calibre Companion which book to read, and in Calibre Companion the series information is recognized.

2)When updating the information in the book file, via "Embed metadata", "Modify epub", the editor or even using "Polish book" again (after having deleted the original_epub format), the number in the last line is changed to: "1.2e+02" which any e-book reader (also the Calibre build in e-book viewer) interprets as 120. To make it clear: the third line is changed to:
<meta refines="#id-3" property="group-position">1.2e+02</meta>

There seems to be a number type problem here, that exists not in the original series_index number metadata definition.
The only way I found to rectify this, was by converting the book again to epub, then the original two lines are used again and everything is fine.

I would like to suggest a modification to "Polish book": Just leave the series information in the original version.
Should that not be possible, then all the other possible interactions with the bookfile have to be changed to use a correct number format.

Otherwise "Polish books" is wonderful, I run it on all my .epub ebooks that I add to calibre.