Bound variable cannot be set as parameter of method in Guided rule editor, when another variable is bound to attribute of class

Description of problem:
As in the summary.

Version-Release number of selected component (if applicable):
BRMS 6.0.1.CR1

How reproducible:
Always

Steps to Reproduce:
1. Add import (for example java.lang.String) to project. (Tools -> Project editor -> Import Suggestions)
2. Create new Guided rule (New Item -> Guided rule) and add import to rule (Config -> New item).
3. Set 'when' section to looks like this 's : String( l : length)'.
4. In 'then' section, call method on 's' and select method, which has parameter with at least one String parameter. (It is important to select method, where it is possible to use bound variable.)

Actual results:
Bound variable cannot be selected.

Expected results:
It is possible to select bound variable.

Additional info:
Also you can do that this way:
1. Make this rule in Guided rule editor:

rule "testrule"
when
s : String( )
then
s.concat( s );
end

2. Try to change 'when' section to 's : String( l : length)'
3. Then section completely disappear.