This was a hand from one of my tables. The Button had pretty good PT numbers, 16/11/3, and always appeared to be a very decent player. But I don't understand this play. Is there any reason to do this, other than just to commit himself to the pot? UTG+1 is a solid, tight player.

Poker Room skin
No Limit Holdem Ring game
Blinds: $0.50/$1
10 players


Stack sizes:
UTG: $97.20
UTG+1: $98
UTG+2: $112.30
MP1: $94
MP2: $102.30
MP3: $98.50
Pozzo: $100
Button: $105
SB: $224.20
BB: $100

Pre-flop: (10 players)
UTG raises to $5, UTG+1 calls, UTG+2 folds, MP1 calls, 2 folds, Pozzo folds, Button calls, 2 folds.

Flop: ($21.5, 4 players)
UTG checks, UTG+1 bets $5, MP1 raises to $15, Button calls, UTG folds, UTG+1 raises to $45, MP1 folds, Button raises to $75, UTG+1 calls.

Turn: ($186.5, 2 players)
UTG+1 is all-in $18, Button calls.

River: ($222.5, 1 player + 1 all-in - Main pot: $222.5)


Results:
Final pot: $222.5
UTG+1 shows
Button shows

Also, wtf is UTG+1 doing flat calling on the flop? Just push the rest in for Christ's sakes, you have the current nuts.