I had a bit of a chuckle that apparently 5 out of 50000 opening "(" parentheses weren't closed, but then I saw that 2 out of 12000 "]" brackets weren't opened! What criminal is using these standalone?
Hahahah... Yes, contributing to the frequency tables. At least we're not including the symbols in question in our comments, so as not add to the imbalance!
Mixing them should be relatively common when denoting intervals, as in "(a, b]" or "[a, b)", so that'd be one cause for being unbalanced. But even so, the math on their usage still doesn't add up.