When using KCalc, using the numpad (right side of arrow keys) has no effect. The inputs must be either entered by using the mouse or by using the row of number on top of the QWERTY side of the keyboard.
The state of numlock was confirmed to be on/set.
Steps to Reproduce:
1. Open instance of KCalc
2. Try to use the numpad keys to perform normal operations
Digits and arithmetic operations would be entered and KCalc's user interface displays the current state (e.g. pressing 7, 8, 9 on the numpad would show the number 789 on KCalc's display).
I tried this in all modes (e.g. simple, scientific, statistical, etc).
I can reproduce this bug on Archlinux:
KDE Apps 15.04.1
KDE Frameworks 5.10
*** This bug has been marked as a duplicate of bug 344638 ***