Enabling Edit Tab Ribbon Controls for List New/Edit forms in SharePoint 2010

We are using Custom Master Page for SharePoint 2010 In the NewForm.aspx When creating a new item and selecting the "Comments" field (which is a Multiple Line type column) a thin portion of the ribbon tabs are exposed just under the webpart title. If a user select any of the other field such as Title, or Date then it is fine.

This is an out of the box “NewForm.aspx” NOT a Custom Form.The problem is only for this Comments (multiple line field) when it is selected, not with any other field.

The problem is only if we apply the Custom Master Page. If disable the Custom Master Page and apply the v4.master page then the problem is resolved.

So it looks like that the Custom Master Page creating the issue:

When I disable the Custom Mater Page and apply the v4.master page then at works fine as following: