Hi Mark,
Thanks for posting in the forum. According to our development experience, the issue looks most likely that APNSoft has overlooked nested positioned elements. Take the following example:
Code: HTML/ASPX
<div style="position:absolute;top:10px;width:10px;height:10px;">
<div style=style="position:absolute;top:10px;width:10px;height:10px;">
</div>
</div>
In this case, the top of the inner DIV will actually be 20px because the outer DIV is a positioned element, thus defines a new coordinate space. In your case, our slide menu pane is similar to the outer DIV, where as the inner DIV is positioned by APN's DataGrid. When they calculate the position and want to position an element to "20px", they must take into consideration any possible positioned element outside and adjust accordingly. As demonstrated in the example above, in order to display the inner DIV at "20px", its top must be set to "10px".
Since CustomItem is a simple container control, most of the time it’s impossible for it to perform special logics to workaround what you put inside because we have no idea what you put in there. Another reason that it makes sense for APN to address it is because they know the internal work of their DataGrid the best. So even if we were to find a workaround for it, it may break when they release their next work.
Thus we would recommend you to get APN involved with this and see what they can do. We will be happy to work with them together to bring a workable solution to you.
Thanks