In org agenda mode, select several items, mark them with
m, then set the todo status
B t to none. Normally I can remove TODO status with
t SPC but
B t SPC isn't permitted.
After a glance at the code I think the 'fast-todo-selection' does not go together with agenda bulk marked items, yet.
Possibly you want to file a report on the org mode mailing list so the issue might be addressed.
As workaround I propose to customize variable
You can use
SPC as character and
(lambda nil (org-agenda-todo "")) as function.
With this setting
B SPC removes the todo states of the marked items AFAICS.