> "Is this the only exception ..."
There are no exceptions. "Spread Level Pro" is an ordinary indicator. It calculates its values and rises signals at every bar.
for example, let's have 10 points spread.
If you set "Spread Level Pro" to allow trading when the spread is higher than 9, it will be satisfied and allow all entries for the other indicators. However, if you set it to trade only when the spread higher than 12, it will prevent all entries simply because the indicator condition will not be satisfied. This behaviour is valid for every indicator.
The "Spread Level Pro" indicator is useful only in live trading because the spread usually changes. The indicator will allow entries when its logical condition is satisfied. It may be satisfied for some entries and not satisfied for others because the market spread can be different. On the other hand, during backtesting the spread is constant. The effect from that is that the indicator's logical rule will be either satisfied or not satisfied for every entry for the backtest.