Strange style loaded when wrap my div in another div why?

Hello everyone, I have an issues with styling. For some reason when I wrapped my div inside another div, some style (style="height:400px") is added to my page and this how it looks like when I inspected element in googlechrome:
<div id="mapDiv" class="map" data-basemap="topo" data-zoom="6" data-scale="9244648.868618" data-loaded="" style="height: 400px;"> When I don't wrap it in another div, here is the html I got:
<div id="mapDiv" class="map" data-basemap="topo" data-zoom="6" data-scale="9244648.868618" data-loaded=""> The html markup is just like this when div is wrapped around the #container
<div> <div id="container"> <div id="mapDiv"></div> ...