The value itself works fine in 10.0, it's not even big on the today's standards.

innodb_buffer_pool_size=384M:

MariaDB [test]> select @@innodb_buffer_pool_size;
---------------------------

---------------------------

---------------------------
1 row in set (0.00 sec)

MariaDB [test]> select @@version;
----------------------

----------------------

----------------------
1 row in set (0.00 sec)

innodb_buffer_pool_size=1G:

MariaDB [test]> select @@innodb_buffer_pool_size;
---------------------------

---------------------------

---------------------------
1 row in set (0.00 sec)

MariaDB [test]> select @@version;
----------------------

----------------------

----------------------
1 row in set (0.00 sec)

Considering that your machine has 1Gb RAM, it is not surprising that you couldn't set the value. Some default values got increased comparing to 5.5, so the most likely reason was that you just did not have enough memory to run it this way. If innodb_buffer_pool_size is important for you, you need to reduce some other values.

Well, I can tell you that I have the value set to 512M right now under Maria 5.5. Also, according to the documentation, you should be able to set the value to as much as 80% of your total memory.

So, I still think that there is some issue in Maria 10.

Ah, sorry. I overlooked the part of your response that said that other default values were increased. Maybe that is the real issue. It could be the combination of the various values.

That's right, the combination of values. You can run SHOW VARIABLES, see buffer sizes, and sum them up to get a rough estimation.

Regarding documentation suggesting 80%, I guess technically it could be made more accurate, but it would have to go into too much detail. It just does not take into account low-memory configurations.
The default configuration and general advice assume that modern versions are run on relatively modern configurations. If you use 5.1, 80% of 1 Gb is probably fine. If you use 5.5, 80% of 2 Gb will probably work. If you use 10.0, it's reasonable to expect that you have more memory, even standard modest laptops are nowadays 4 Gb. You can still run it with less memory, but you have to perform some configuration adjustments.