#1 Original Report
The ABM remove filter dialog will capture the input of the ABM trigger key. Don't get what I mean? Follow those steps:
How to reproduce

Change the ABM trigger key to some letter, like, in my case, 'F'.
Hold 'F' to activate ABM, then click on "pick remove filter".
A dialog will open, with an input textfield where one can search.
The textfield is instantly filled with (i.e.) "ffffffffffffff".

Suggestion

Don't activate typing until the ABM trigger key was released. This may not be easy to do, as I believe that Java on not-Windows won't know "Key pressed/released" events, but only "Key typed".

#2
True, this is not an easy to get bug,
as the focus changes between windows,
it maybe hard to get a common state saving between the windows.

Maybe the advanced build mode should not require the key to be pressed all the time,
what about a 'tapping' to enable disable it?
(Like a 'switch' key)

#3
ABM could perhaps be placed on a toggle hotkey,
Also, improving the selection process to select the desired block might help, originally it was planned to base the block type on the currently selected block in the hotbar.

#4
The same goes for the template saving dialog.