Hi Yuan Lin, thanks for reporting this. Yes, this is because of the recent addition you are referring to, which I find a bit problematic, even though I understand the intent.
It is good to be able to navigate the agenda commands dispatch window but losing the SPC key is too high a price for this. I have pushed a change that advertize the use of C-v and M-v to scroll up and down in export/agenda/attach dispatch buffers, while SPC and DEL are still usable for the export dispatch buffer. >From latest master, you can reuse SPC as a key binding for a custom agenda command. Thanks for reporting this, -- Bastien
