The problem is that the rule
.x-border-box .x-reset,.x-border-box .x-reset * {box-sizing:border-box;-moz-box-sizing:border-box;-ms-box-sizing:border-box;-webkit-box-sizing:border-box;}
somehow applied to all elements of the page, as well as to enter Twitter Bootstrap (tested on FF, Chrome). Therefore, you should simply provide
box-sizing:content-box !important; -moz-box-sizing:content-box !important; -webkit-box-sizing:content-box !important;
for all Twitter input. Additional information about box-sizing .
I hope this helps.
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