Maybe a problem with your transitions.ini config.

The original values for the application section are

[home]

radius = 12

radius_more = 16

saturation = 0.8

brightness = 0.4

zoom = 0.93

zoom_applets = 0.85

transitions.ini can be found at /usr/share/hildon-desktop/transitions.ini. Please make a backup before editing.

Referenced from - http://wiki.maemo.org/Customizing_Maemo#Transitions