Please attach a sample survey which we can use to reproduce the error and provide step-by-step instructions how to reproduce it.

To reproduce the issue:
Note the uploaded survey is set to be presented Question by Question, the conditions for question 2 are the following:

Question 1: Select a fruit [Group of checkboxes] (qid71) equals Pear (pear)
OR
Question 1: Select a fruit [Group of checkboxes] (qid71) equals Apple (apple)

Question 2 should be displayed when either Pears or Apples are selected in question 1. It is only displayed when both options are marked which is wrong.

If the survey is set to the "group by group" or "all in one" formats, the logic works as it should.

I can reproduce the issue with the attached survey.

Hello, recently we have noted that the group by group presentation format also contains a faulty logic evaluation. It seems that when the logic needs information from questions across different pages, the OR conditions get evaluated as AND.
The logic works correctly only when the questions that define another question's conditions are displayed on the same page and are evaluated via javascript.

thx for the detailed information, I'll work on this asap.

Could you please clarify which versions are affected? Is the current build still buggy ?

Fixed in rev 7549.
Many thanks for this bug report.