Calibre is deleting Series field even when it's not being modified
This is a serious bug and has lost me metadata twice now.
1) Select some books that have Series field filled.
2) Hit "E" to edit metadata
3) Type something into Series filed
4) Delete it (as if you've made a mistake and wanted to modify some other field).
ALL of your Series data is now completely lost. I presume all other fields are susceptible to this flawed behavior.
Calibre 1.8, running on OS X.