Hello,
when I set the default value true, it is well managed in my filter but the displayed value is always equal to false.
<BooleanInput
source="account.active"
label="active"
defaultValue={true}
/>

I think it's a bug. Same problem with NullableBooleanInput.
Other information:
Environment
It does work for me: https://codesandbox.io/s/0q6583162p
Look at the Post Creation form, the "commentable" boolean input.
Do you have a bit more context ? Which version of Material UI do you use?
@Kmaschta it seems to be in the context of a Filter form
Yes I also tested on the sandbox and it works.
In fact the default value does not work when the source is an object, for example account.active.
Interesting clue: it seems to be working on RA 2.3: https://codesandbox.io/s/l5wknxqmwq (see the Post List filters)
I'm trying to figure out how to make RA 2.5 work on CodeSandbox.
OK ! I managed to get RA 2.5 working with CodeSandbox thanks to Fran莽ois.
Here it is, on the PostList, there is a BooleanInput as a filter with defaultValue is true: https://codesandbox.io/s/y0xx53yy0v

And it seems to be working.
Do you know what can be different from your codebase?
As mentioned above, the default value does not work with BooleanInput and NullableBooleanInput when the source is an object,
for example accounts.commented.
Show https://codesandbox.io/s/k3lq8j87v5
I can't reproduce this issue anymore on V3. Feel free to reopen if I'm wrong
Most helpful comment
As mentioned above, the default value does not work with BooleanInput and NullableBooleanInput when the source is an object,
for example
accounts.commented.Show https://codesandbox.io/s/k3lq8j87v5