Note that the length of the concatenation of 'packet_length', 'padding_length', 'payload', and 'random padding' MUST be a multiple of the cipher block size or 8, whichever is larger. This constraint MUST be enforced, even when using stream ciphers. Note that the 'packet_length' field is also encrypted, and processing it requires special care when sending or receiving packets. Also note that the insertion of variable amounts of 'random padding' may help thwart traffic analysis.
Emphasis mine. I am aware that the padding contents themselves are required to be random, but does OpenSSH itself use random padding lengths for any cipher modes? The padding length field itself is encrypted for some modes. Looking at the source, it doesn't look like it uses padding of random lengths, but I am not particularly familiar with the internals of OpenSSH.