I've been playing since ARR was released, and prior to FFXIV i played FFXI. I grew very accustomed to the key mappings of FFXI and so i've replicated what I've used into FFXIV.
On the numpad, 8, 4, 6, and 2 are up, left, right, and down (respectively). 0 on the numpad is mapped to interact with the closes object and "use" it. So I use 0 to target the closest NPC, closest enemy, the summoning bell, etc... I also use 0 on the numpad after selecting something to open the menu for it. I have Shift plus those same directional numpad keys mapped to navigate menus, so if i hit - on the numpad to open the menu, i'll hold shift and use 8 and 2 to move up and down, 0 to select a menu option.
The arrow keys are mapped to move my view so that i can move my character with the numpad and the view with the arrow keys.
The problem: This has been an issues ever since i first started playing the game and the issue continues today. When using the numpad and/or the arrow keys, for no reason at all I will enter typing mode and my character will stop receiving my commands. I will not be aware of this until i look at my chat log to see 8's, 4's, 6's, and 2's littering the text entry field. This is especially problematic when im fighting a dungeon boss and its time to move out of the way, but suddenly my attacks arent registered, so then i have to hit escape a bunch of times or backspace to get rid of all of the numbers, or even just hit enter to send the text to party chat or whatever chat I happen to be on.
If you map your keys the same as me, im quite sure you'll be able to replicate this with a short bit of game play. I would say within 30 minutes of actively using this, it'll happen at least once. It happens to me far more often than that, but as we all know, when we seek help on an issue, it seems to hide itself. I've replicated this since ARR's release on 3 PC builds (1 complete rebuild, including keyboard and mouse) and 2 laptops (with several other upgrades over time).
Is this a known bug? I've searched and cannot find it. I've played on everything from Windows XP to Windows 10, the issue happens across all.