Defining a boolean parameter will not return a boolean value as expected, but a String value.

Defining the parameter:{{}}

parameters { booleanParam(name: 'bForceCheckout', defaultValue: false, description: '') }

Checking the type...

println bForceCheckout.getClass()

...will give you:

09:06:03 class java.lang.String

This of course leads to some nice behaviour when checking the variable in conditions...