Hello,
I use Opera 9.64 on Linux.
When I edit tags (both retagging a question and tagging a brand new question (like this one)) the tag suggestion dropdown updates messes with focus of the text input field.
When new suggestions are displayed the cursor switches to the beginning of the text input field. If I type manually the rest of the tag that I want (rather than accepting one of the suggestions with a mouse click or whatever), I'll just prefix the first tag I've typed.