Multiple X sessions plus desktop effects cause blank KDE4 desktop

[TC]

Binary package hint: kdebase-workspace

Hello,

KDE4 using desktop effects works great on Intrepid for one instance of X and KDE, but any additional instance of KDE with desktop effects enabled started shows only a blank screen. The problem only occurs when desktop effects are enabled with OpenGL chosen as the compositing type. It does not matter if a different user is launching X or whether they are launching through startx or KDM - if desktop effects are enabled in one KDE session and another is launched the additional session is blank and unusable (unless desktop effects are disabled for the new session).

In other words, one session per machine can use desktop effects and afterwards any session that tries just results in a blank screen, similar to the one described in #182288. I do not believe this is a duplicate bug. (This bug == desktop effects work once, that bug == desktop effects work never)

Steps to reproduce:
1. Start KDE4 session as any user with desktop effects enabled and OpenGL selected as compositing type.
2. See that desktop effects function properly.
3. Repeat step 1.
4. See that the new session is blank/black for the most part.
5. Switch to the first session.
6. See that it still is functioning properly.

Expected behavior:
1. Start KDE4 session as any user with desktop effects enabled and OpenGL selected as compositing type.
2. Start another KDE4 session as any user with desktop effects enabled and OpenGL selected as compositing type.
3. Both sessions work.

I am using the Intel X driver. lspci shows my video card as:
00:02.0 VGA compatible controller: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (rev 0c)
00:02.1 Display controller: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (rev 0c)

If there's any other information that might be useful, I'll be happy to append it.