Numerous people have reported in the past, that the Shift key does not freeze the Word Analysis Window when using BibleWorks 7 or 8 on Parallels 6, 7 or 8. This bug has been present since at least 2008 (see posts here, here and here) This does not happen when running BW in VMware or VirtualBox. Looking through the BW forums it was suggested to use the Option/Alt key as a work around. I used this for months, but was never satisfied with it as you had to click the Browse Window again to continue updating the Word Analysis Window.
While looking for a solution in the Parallels forums, I found out, that the bug is caused by a faulty way of handling the Shift Key in Parallels Desktop. It is a known issue as admitted by Parallels staff: "PD delays shift until other key is pressed as it is a part of some shortcut which should not go to VM." Even though promised by them this has never been fixed in the default installation of PD, as I still had the problem after upgrading to PD8.
There is a simple solution, though, which I have not seen mentioned in the BibleWorks forum. Just change the settings for your VM as follows: In the Parallels Desktop menu go to 'Virtual Machine' --> 'Configure...'. Then in the configuration dialog click on 'Options' then select 'Advanced' and then activate the Option 'Optimize modifier keys for games'.
I eventually found a Parallels Knowledgebase article with screenshots about this, which in spite of the title, also applies to BW: Problems with Ctrl, Alt, Cmd, Shift and other modifiers in games http://kb.parallels.com/en/7072
I hope this helps someone. Please let me know, if it works for you.