How to get Flex Builder 3 and Eclipse 3.4 Ganymede to play nice

There are a lot of good things I can say about Eclipse, but I have two griefs: One is the fact that I have way too much stuff in the menus that I never use. The other is that I’ve spent way too much time fiddling with the installation of plugins. Yesterday was no different: Upgrading to Ganymede left me without a working Flex Builder plugin. The MXML editor simply breaks with a traceback:
org.eclipse.jface.util.Assert$AssertionFailedException: Assertion failed:
at org.eclipse.jface.util.Assert.isTrue(Assert.java:185)
at org.eclipse.jface.util.Assert.isTrue(Assert.java:170)
at com.adobe.flexbuilder.editors.derived.editor.FlexMultiPageEditorPart.setActivePage(FlexMultiPageEditorPart.java:569)

I did find a solution here (make sure to restart eclipse with -clean afterwards), but this kind of fiddling with the installation is not something I should have to do. Especially not with a plugin that’s as important as Flex Builder. Adobe, I’m looking at you!