Steps to replicate :

1.Create new javascript file.
2.Type 3 lines in editor:

window.variable.num1
window.variable.num2
window.variable.num3

3. Press CTRL+F to open Find/Replace dialog
4. Type “variable” in “Find” text field
5. Type “anotherVariable” in “Replace with” text field
6. Press “Replace/Find” button – “window.variable.num1” is now replaced with “window.anotherVariable.num1” – CORRECT!
7. Press “Replace/Find” button – “window.variable.num2” is now replaced with “anotherVariableariable.num2” – INCORRECT!
8. Press “Replace/Find” button – “window.variable.num3” is now replaced with “anotherVariableariable.num2” – INCORRECT!

CodeMix
Version 2018 CI 2018.4.18
Build Id: 0.9.0.201804180845

Spring Tool Suite
Version: 3.9.1.RELEASE
Build Id: 201710111144
Platform: Eclipse Neon.3 (4.6.3)