No result with SendKeys to IE8 using Selenium on BrowserStack - unit-testing

Question

I'm using Selenium to perform testing on BrowserStack, and have hit a problem while testing IE8.
I've found that when I target elements and then call Click, the full effect of the action is not being undertaken*.
Through trial-and-error I found that if I call Click twice then the expected action is undertaken.
However, one of the testing steps involves writing a number to a text field, and for this I have the following:
driver.FindElement(By.CssSelector("...")).Click();
driver.FindElement(By.CssSelector("...")).Clear();
driver.FindElement(By.CssSelector("...")).SendKeys(Keys.NumberPad1);
driver.FindElement(By.CssSelector("...")).Click();
But "1" never appears in the field. I can tell it never appears because I'm capturing screenshots after each step; I can see that the field gets highlighted (as the active element) and I can see the cursor inside the field, but no result from the method call.
Furthermore, I've even tried giving the field an ID and addressing it with
driver.FindElement(By.Id("txtCountManual")).SendKeys(Keys.NumberPad1);
But with the same (lack of) results.
Does anyone have any suggestions as to how I may send a textual value to a field in IE8 using Selenium and BrowserStack?
* The "expected action" involves using Knockout.js to display a selected value in another element. So for example, I found that if I programmatically click a radio button and then take a screenshot, I can see that the radio button has been clicked but the action performed by Knockout.js has not taken place; if I click the element a second time then the Knockout.js action is performed. This double-clicking is not required when I manually test using IE8 via BrowserStack.