A problem about @Throws at kotlin

Language Design
1

I write a custom Exception

class ConnectionException(reason: String) : KtproxyException(reason)

and the KtproxyException is based on Throwable.

then I write a function

@Throws(ConnectionException::class, IOException::class)
    override suspend fun write(data: ByteArray) {
        if (isClosed) throw ConnectionException("connection is closed")

        val cipher = encryptCipher.encrypt(data)
        val frame = Frame(FrameType.CLIENT, FrameContentType.BINARY, cipher)
        proxySocketChannel.aWrite(ByteBuffer.wrap(frame.frameByteArray))
    }

When I write codes in idea ue 2017.3.4, I type Ctrl + Q and it says my function will only throw IOException.

I wonder it’s a bug of kotlin or idea ue.