`BorrowingIteratorProtocol` false positive?

Using Swift
1

I am hitting a compilation error, which I think is a false positive, attempting to upgrade some code to use BorrowingIteratorProtocol since it compiles fine if I remove the first condition from the if statement (tested with the 6.4.x-snapshot-2026-08-14, nightly, and devsnapshot toolchains on Arch Linux).

Is it actually a false positive, if so I'll open an issue on github, or am I holding it wrong?

Godbolt for small reproducer.

small reproducer 
struct BitSet: Sendable {
    typealias Element = UInt64
    fileprivate var storage:Element
}

extension BitSet {
    func makeBorrowingIterator() -> BorrowingIterator {
        .init()
    }

    struct BorrowingIterator: BorrowingIteratorProtocol {
        @_lifetime(borrow self)
        func nextSpan(maxCount: Int) -> Span<Element> {
            .init()
        }
    }
}

let set = BitSet(storage: .max)
var smallestValue:UInt64! = nil
var iterator = set.makeBorrowingIterator()
while true {
    let iteratorSpan = iterator.nextSpan()
    guard !iteratorSpan.isEmpty else { break }
    for i in iteratorSpan.indices {
        if smallestValue == nil || iteratorSpan[i] < smallestValue! {
            smallestValue = iteratorSpan[i]
        }
    }
}
compilation error 

22 | var iterator = set.makeBorrowingIterator()
23 | while true {
24 |     let iteratorSpan = iterator.nextSpan()
   |         |              - note: it depends on this scoped access to variable 'iterator'
   |         - error: lifetime-dependent variable 'iteratorSpan' escapes its scope
25 |     guard !iteratorSpan.isEmpty else { break }
26 |     for i in iteratorSpan.indices {
27 |         if smallestValue == nil || iteratorSpan[i] < smallestValue! {
   |                                                                   - note: this use of the lifetime-dependent value is out of scope
28 |             smallestValue = iteratorSpan[i]
29 |         }

Edit:

small statement workaround that successfully compiles 
if smallestValue == nil {
                    smallestValue = iteratorSpan[i]
                } else if iteratorSpan[i] < smallestValue! {
                    smallestValue = iteratorSpan[i]
                }

github issue