The tourists comfortably beat the county side by 100 runs after amassing 358 for seven in their 50 overs on Saturday.
Kent were 176-3 in reply in the 30th over when Alex Blake, on 89, skied a return catch to Ali, who was bowling.
Video footage emerged on Monday that showed the seamer appeared to floor the catch.
The 24-year-old appeared to attempt to regather
the ball with his right hand, failed to do so, and then went into his
trademark celebration anyway - bringing both hands to his chest, curling
his torso down and then bursting out into a star shape.
what had happened behind him, Blake continued his march off the field
for 89. While his batting partner, Ollie Robinson, protested the catch,
he was unable to convince the umpires to overturn the dismissal.
The laws of cricket state that a catch is completed only when "a fielder
obtains complete control over both the ball and his/her own movement".
The image of Pakistani cricket was damaged by a spot-fixing controversy that blighted their England tour in 2010, with three players handed bans from the game.
Pakistan announced on Monday that veteran batsman Shoaib Malik has returned home to deal with a personal issue but is expected to rejoin the team in 10 days' time.
"The PCB will not be making any further comments and fully expects all concerned to respect Shoaib's privacy," the Pakistan Cricket Board said in a statement.
Pakistan are playing one Twenty20 match and five one-day internationals against England before the start of the World Cup in late May.