Oh!
The following is the source code of “WebUI.setText” keyword:
At Line#53, it explicitly calls WebElement.clear() method.
...
WebElement webElement = WebUIAbstractKeyword.findWebElement(to)
logger.logDebug(MessageFormat.format(StringConstants.KW_LOG_INFO_CLEARING_OBJ_TXT, to.getObjectId()))
webElement.clear()
...
This code calls WebElement.clear() to clear, as documented, the previous values. But unfortunately, for some reason, it does not work. All I want to say here is that Katalon Studio is not really causing the problem. The cause lies in the WebDriver & browser layer.
You should have a wider scope of search for workaround. Even in this Katalon User forum, you can find several posts related to “WebUI.setText”. For example: