SUMMARY
KDE Partitionmanager seems to somehow mess with my trackpad driver (synaptics). When I tell it to apply changes, my mouse pointer becomes much slower for a while, like it's switching to a different driver.

* I did not find anything suspicious in dmesg
* It doesn't matter if it's an internal or USB drive

STEPS TO REPRODUCE
1. Create a new partition layout
2. Click "Apply"

OBSERVED RESULT
The behaviour of my trackpad changes

EXPECTED RESULT
Partitioning drives shouldn influence the trackpad. They've got nothing to do with each other.