remove files from books works inconsistently

[Dylan Urquhart]

When in list view, Right Clicking on a book

Navigating to Remove Books > Remove Files of a Specific Format From Books

brings up a menu of a book with 2 formats, one MOBI, the other PDF

Clicking the MOBI edition, and pressing OK does not remove the MOBI edition from my library. No error message given.

HOWEVER

Navigating to Remove Books > Remove all formats from selected books... except

bring sup a menu of the same 2 formats, MOBI and PDF

Clicking the PDF edition to keep, and pressing the OK button will remove the MOBI edition from my library.

This has been reproduced multiple times across recent versions of Calibre, with multiple books.

Description: Linux Mint 18.3 Sylvia
Release: 18.3
  Installed: 2.55.0+dfsg-1ubuntu0.2
  Candidate: 2.55.0+dfsg-1ubuntu0.2
  Version table:
 *** 2.55.0+dfsg-1ubuntu0.2 500
        500 http://la-mirrors.evowise.com/ubuntu xenial-updates/universe amd64 Packages
        500 http://la-mirrors.evowise.com/ubuntu xenial-updates/universe i386 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/universe amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/universe i386 Packages
        100 /var/lib/dpkg/status
     2.55.0+dfsg-1 500
        500 http://la-mirrors.evowise.com/ubuntu xenial/universe amd64 Packages
        500 http://la-mirrors.evowise.com/ubuntu xenial/universe i386 Packages