[GNC] Trading accounts functionality

[zuperkoleoptera at gmail.com]

    I've been using gnucash since 2014, recording my personal finances and
investments. I am in Europe so my main currency is EUR.
Up until now my investments were in EUR currency as well as some
crypto, which are again expressed in EUR currency.

Lately I started building an investment portfolio in USD, so I started
exploring the trading accounts functionality. I have read both articles
from P. Selinger and browsed through the documentation and mailing
lists, for related subjects.
The problem I am facing is the following, after activating trading
accounts the system created the hierarchy for all the trading accounts,
but also created a bunch of splits in already recorded transactions. So
from the beginning the trading:currency:EUR account has a balance of
almost 2.300 eur and includes all my transactions related to my crypto
portfolio. 
Is this normal for the trading system to create splits in already
recorded transactions? And what does it mean for the
trading:currency:EUR to have a positive balance of 2.300 eur, is this
exchange realized gain?