Sorry for being picky, trying to understand the real issue as I can't test it.

As for supporting null for bit, http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.dc38151.1530/doc/html/san1278453534056.html says the bit datatype only supports 0 and 1 for SQL Anywhere. Not sure if the null support is a new addition or not.

Now, I would like to understand exactly how your data are mapped.

From what I see in the Hibernate source code, we should have:
Java boolean -> SQL Anywhere boolean
Thus my question about if you have a boolean datatype in SQL Anywhere. I can't find one in the documentation.

Could you try to create a table with a SQL boolean column in your database and see what id does? Does it create a boolean column? Is it converted to bit?

From what I understand from your mapping, you have:
Java boolean -> SQL Anywhere bit
Am I right about that or did I misunderstand?

Personally, I would vote for mapping Java boolean to SQL Anywhere tinyint, exactly as we do it for Sybase. That would avoid all the issues to date. But sure, you would have to change your schema to make it work.

BTW, I pushed changes to https://github.com/hibernate/hibernate-orm/pull/2625 as I forgot about something.