I’m not experiencing this here, but I do notice a similar bug, so I’m wondering if it’s related. Just like you I start a new message and enter an XMPP recipient’s name. For contacts that are only associated with XMPP I can immediately write them an XMPP message and send. However, if there are other ways to communicate with them (e.g. SMS) then a list appears at the top of the page and I have to choose the XMPP address.
For me, that all works fine. However, if I have no SIM card, I notice that choosing a non-XMPP way in the first instance means that I then can’t switch to using XMPP afterwards in the way you describe.
So this sounds similar, but not the same. Do you have a SIM card in the device?