Eclipse Losing Reference to JARs

I have this weird problem that every once in a while (especially upon checking in files to SVN/CVS but not limited to that situation) Eclipse will lose reference to class path JARs and start signalling errors everywhere in the code.
What I temporarily did to fix this was to remove a library directory from the [Project] Properties --> Java Build Path --> Source list of a project, save the properties, open them again and add it back in. Problem gone... for a while.

Now I'm trying something I read somewhere: start Eclipse with the -clean command line parameter.

I'll keep you posted...

Feb 2010 Update: with the current version of Eclipse I'm using (Eclipse Java EE IDE for Web Developers, Build id: 20100218-1602) this issue seems to be vanished.

Booting Debian in Text Mode

# disabling login GUI (if not gdm replace with yours)
> update-rc.d -f gdm remove

# re-enabling
> update-rc.d -f gdm defaults

No Javadoc When Hovering Cursor Over Text in Eclipse

I had this weird problem that no javadoc preview showed up when hovering the cursor over java code in Eclipse.

Eclipse version: eclipse-java-ganymede-SR2-linux-gtk
OS: Linux (Fedora 11)

I didn't find out why it didn't work but I found out that it was specific to the version of Eclipse I was using.
When I upgraded to Eclipse Galileo (eclipse-java-galileo-linux-gtk), with exactly the same configuration files and preferences, it worked straight away.

I guess it was a bug of the Ganymede SR2 then...