On the GNU APL web page, it states that GNU APL has a maximum symbol count of 65536. However, it appears that this isn't enforced, and you can make as many symbols as you like. If you make a million or so, and type )VARS, the system will segfault.
This isn't anything a user is likely to encounter in a real world application, so it isn't really a bug. But it is a small difference between what the system does and what the documentation says.