I have updated to KDE 4.10.0 and compiled qt-core-4.8.4-r2 with -Os. Plasma-workspace is rebuild, but I can't see any running tasks like kontact or dolphin in the systray. Other like console or firefox are seen in the systray. I found temporary workaround (very temporary), if You go to system settings, desktop effects, advanced and switch qt graphics system to opposite, then refresh this change triggers, will fix task manager for a while (until You log off). Reproducible: Always
*** This bug has been marked as a duplicate of bug 314830 ***