I have several time been bitten by ST3 deleting a parenthesis to the right of the cursor, when deletion to left is happening, leading to unbalanced parentheses. I illustrate the sequence below, where [C] stands for the cursor. Deletion is accomplished by hitting Backspace.
if (identical(dfr, dfr0)[C]) {
=>
if (identical([C]]) {
=>
if (identical[C] {
As you can see, the parentheses started out balanced, but at the last Backspace ST3 deletes both the parenthesis to the left of the cursor and the one to the right, assuming, I suppose, that they are paired–which they are not, in this case.