qtip close button appears multiple times

I have using qitp 2.0 for one of my project.
I have customized close button in tool tip.
Some times tool-tip entry close button appears multiple times.
Please help how to solve this issue!.
I have attached screenshot for your reference.
HTML:

<a class="yellow" title="&lt;b&gt;Title:&lt;/b&gt; summary text."><span class="bold">cell membrane</span></a>

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CSS:

.yellow {
white-space:nowrap;
cursor:pointer;
color: #15806b;
font-weight: bold;
text-decoration: none;
}

.myCustomClassWithBgPNG {
width: 16px;
height: 16px;
position: relative;
left: 95%;
top: -10px;
background-image: url("images/unit5_close.png") !important;
background-position: center !important;
background-repeat: no-repeat !important;
}

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JS:

$('.yellow').qtip({content: {attr: 'title', title: {button: $('<div/>', { 'class': 'myCustomClassWithBgPNG' })}}, style: {classes: 'qtip-dark qtip-shadow'}, show: {event: 'click'}, hide: 'unfocus', position: {my: 'bottom center', at: 'top center'}});

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screenshot1.png