CEWP removing “value” attribute in input tag

I am using Content Editor WebPart in SP 2010 to create a simple button control, using the following code:

<table class="ms-rteTable-6" align="center" style="width: 560px; height: 130px; text-align: center"><tbody><tr class="ms-rteTableHeaderRow-6"><th class="ms-rteTableHeaderEvenCol-6" style="width: 122px; height: 14px"><input onclick="window.open (&#39;/sites/XXX/YYY.pdf&#39;)" type="button" value="Doc1"
                        style="width: 235px" /></th><th class="ms-rteTableHeaderOddCol-6" style="height: 14px"><input onclick="window.open (&#39;/sites/XXX/YYY.pdf&#39;)" type="button" value="Doc2"
                        style="width: 235px" /></th></tr><tr><th class="ms-rteTableHeaderEvenCol-6" style="height: 14px"><input onclick="window.open (&#39;/sites/XXX/YYY.pdf&#39;)" type="button" value="Doc3"
                        style="width: 235px" /></th><th class="ms-rteTableHeaderOddCol-6" style="height: 14px"><input onclick="window.open (&#39;/sites/XXX/YYY.pdf&#39;)" type="button" value="Doc4"
                        style="width: 235px" /></th></tr><tr><th class="ms-rteTableHeaderEvenCol-6" style="height: 14px"><input onclick="window.open (&#39;/sites/XXX/YYY.pdf&#39;)" type="button" value="Doc5"
                        style="width: 235px" /></th></tr></tbody></table>

However on saving, the "value" tag vanishes leaving behind a blank looking button. The button continues to function as expected.

Has anyone experienced this?