Incorrect quote removal in arithmetic expansion
POSIX XCU 2.6.4:
The expression shall be treated as if it were in double-quotes, except that a double-quote inside the expression is not treated specially. The shell shall expand all tokens in the expression for parameter expansion, command substitution, and quote removal.
This means single- and double-quotes are not special and backslashes are not always special inside an arithmetic expansion.
Fixed in r4081