Seeing the same right now across SOFU.
Only the first tag is suggested. All others, no matter front, middle or back, will not offer tag suggestions.
Even with a cleared and flushed cache.
Since the recent deployment...
Doesn't matter where or which number tag you're trying to put in, first or third or fifth, whenever retagging a few posts on SuperUser, the cursor will always jump back to the first position and replace whatever is the first word. Annoying when trying to create even a sensible list of just three tags.
Doesn't feel like proper behaviour at all.
Workaround for Opera
One way to deal with this in Opera is to type the tags backward.
Type in one and when you're done, hit Home or whatever your keyboard of choice does to get you back to the start of the input area. Then type a space and go back again to the front of the input. Now type up the next tag and it will suggest it and prefill it properly. Return to the front and pad with that leading space for each tag you want to include