RDP connection via application access fails when client certificate is set to require

I've set up a VIP with a client SSL profile that requires a certificate. The access policy on this VIP has some resource assignments: network access, rdp application access and rdp via app tunnel access. All of these resources work just fine, except the rdp application access. The connection is not established and the handshake gives this failure:

TLSv1.2 Record Layer: Handshake Protocol: Multiple Handshake Messages
    Content Type: Handshake (22)
    Version: TLS 1.2 (0x0303)
    Length: 269
    Handshake Protocol: Certificate
        Handshake Type: Certificate (11)
        Length: 3
        Certificates Length: 0
    Handshake Protocol: Client Key Exchange

However, another resource works just fine:

TLSv1.2 Record Layer: Handshake Protocol: Multiple Handshake Messages
    Content Type: Handshake (22)
    Version: TLS 1.2 (0x0303)
    Length: 269
    Handshake Protocol: Certificate
        Handshake Type: Certificate (11)
        Length: 3
        Certificates Length: 2647
    Handshake Protocol: Client Key Exchange

In the first capture, the certificate length is 0. In the second one it is 2647.

Now, I've set the client SSL profile to 'request' and all resources work just fine.

Can someone shed some light on this issue? Why does it fail when set to 'require'?