I just tested the little EF-X8 flash on the X-T1 and it only behaves as you describe when RED EYE REMOVAL is ON (note that red-eye removal only works if FACE DETECTION under AUTOFOCUS SETTING is also ON).
Anyway, at page 37 of the X-T1 manual, on reads: "Except in commander mode, the flash may fire several times with each shot. Do not move the camera until shooting is complete."
What really intrigued me is that you're saying you can only find the flash modes red eye reducion and commander. In first place, if you're seeing RED EYE REDUCTION in FLASH MODE menu, it means that RED EYE REMOVAL is ON,
and FACE DETECTION is also ON!
In second place, in any shooting mode I see in FLASH MODE menu the options FORCED FLASH, 2ND CURTAIN SYNC, COMMANDER and SUPRESSED FLASH; under aperture-priority shooting mode, there is also SLOW SYNC (or
RED EYE & SLOW) option available; when the shutter-speed and aperture are in "A" (P mode), AUTO (or RED EYE REDUCTION) option is also available, exactly as you can read in the manual at page 133. I hope this helps!