This usually happens when typing too fast or using a non-standard keyboard.
You have likely activated "Direct Input mode" (often toggled by pressing the Right Alt key). sinhala tamil ime kit for windows 10
: Allows seamless switching between Sinhala and Tamil without interruption to workflow. This usually happens when typing too fast or
[Windows 11/10] How to add/change Keyboard Language | Official Support sinhala tamil ime kit for windows 10