This typically happens due to a styling conflict between your theme and the plugin. You can override your theme settings for the form by going into the Configure Tabs of the plugin and under the Captcha tab, add CSS overrides that will change the form and will retain between upgrades. Example text to place in the CSS override field (copy and paste into the CSS override field all items in red):
/*Style for Registration Form Layout */
#evrRegForm {
width:95%;
overflow:hidden;
}
#evrRegForm .evr_regform ul li {
list-style:none;
padding-bottom:5px;
}
#evrRegForm ul li {
list-style:none;
padding-bottom:5px;
}
.evr_regform label{
font-weight: bold;
display:block;
padding-bottom:5px;
margin-top:10px;
}
/*Textfield style*/
#evrRegForm li .fieldbox {
height:25px;
padding-left:5px;
}
#evrRegForm li .fieldbox input {
height:25px;
padding-top:5px;
width:300px;
}
#evrRegForm li .couponbox {
height:20px;
padding-left:5px;
}
#evrRegForm li .couponbox input {
height:20px;
padding-top:5px;
width:200px;
}
/*Textarea style*/
#evrRegForm li .msgbox {
height:100px;
padding-left:5px;
}
#evrRegForm li .msgbox textarea {
height:100px;
padding-top:5px;
width:385px;
}
/*Radio Style & Checkbox Style*/
#evrRegForm .radio {
margin-top:0 ;
margin-bottom:0;
text-indent: -15px;
padding-left: 35px;
display: block;
}
/*End form style*/