Hi, Norman
Regarding this point
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In RTC, the link type "Tested By Test Case" will always shows the same icon as its shown for TCER( Test Case Execution Record" being passed /failed. It will show the icon of latest result which we call as "Test Case Result" ( TCR). On hovering the link, you will be able to see all previous runs with appropriate results and their icons.
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Krupa is correct that TCER latest result matters, however, if this is the only condition applies here, your comment would be correct that the latest test case result is Passed and then icon should be Passed(green) instead of Failed(red).
I suspect that this test case must have at least two TCERs(one TestCase can have multiple TCERs). You can check the Test Case Results for the specific TestCase and see which TCER the result is from, in particular, pay attention to the Failed Result and Passed. If the Failed result is the latest result for one TCER and Passed result is the latest one for another TCER for the same TestCase, then the severity order plays a role here. That is, Failed (one TCER's latest result) has higher severity order than Passed(another TCER's latest result), then the icon will show higher severity result only, in this case Failed result(red icon) even though the Passed result was run later than the Failed result.