Intended.

Code:

# Kicked or leaving players lose resets
# Players who leave a team will lose an island reset chance
# If a player has zero resets left and leaves a team, they cannot make a new
# island by themselves and can only join a team.

You should have had 1 reset left in your described scenario, however it seems you used one up elsewhere.

 

Just tested this to confirm it works as intended. It does.
Joining doesn't eat up a reset, only leaving and creating an island does.
You definitely lost a reset elsewhere.