Have a basic full-sized >10 year old ps2 Microsoft keyboard. Has a seperate numeric keypad on the right side with a seperate key grouping located between keyboard and number pad for Home/End/Instert/Delete/PageUp/PageDown as well as right/left/up/down arrows. Now for some reason when the NumLock key is activated, this seperate grouping of right/left/up/down arrow keys gets locked out and can't be used to edit documents, scroll dropdowns, etc across applications. Obviously toggling NumLock on/off between number input and document editing/cursor movement is sub-optimal.
Didn't notice this issue before the latest rounds of RC updates, related to groups, etc. Have no idea how it affects this, just never noticed the issue before these latest RCs. Noticed it before the last RC actually, just didn't report, so probably 2-3 RCs back. To confuse matters i've also updated my SCEs within the past week.
Tried numlockx and it didn't help. Booted into TC6 to rule out hardware issue and keyboard then works as expected. Other than routine RC and SCE updates, don't recall making any changes that may affect this behaviour. Maybe someone else can confirm in dCore-jessie, running up to date Xorg, etc:
You are running dCore-jessie:2016.05.03.01.09, the latest release candidate.