Repro Steps:
On 32 bit version of LibreOffice on Windows 64 bit build (W7 x64 here)

1) Install 64 bit Java if not already installed
2) In LibreOffice go to
    a) tools -> options -> advanced
    b) Click "Add... on the right side of the Java box
    c) Select 64 bit path (C:/Program Files/Java/jre7
    d) Click Ok
    e) wait a few seconds to see the new detected version of JRE show up
    f) Select new version shown (make sure the Location below the box reads  "C:\Program Files\java\jre7")
    
3) Setup a new base file
   a) File -> New -> Database
   b) Click "finish"

Observed: You get an error (I've seen two distinct ones, one says JRE defective, the other says No Java installation found)

Expected: Never be able to select a 64 bit version if you can't use it


Minor - not going to prevent high quality work but can slow it down as the user tries to figure out what is going on
Low - not going to affect many people, I think by default both 32bit and 64 bit versions of Java are installed on most (if not all) Windows builds). If you are on Linux and have a 64 bit version hopefully users are installing 64 bit version of LibreOffice