If there is a #region directive within a partial class, it may cause errors during a merge.

partial class classA
{
#region testRegion
int a =1;
#endRegion
}

partial class classA
{
#region region2
int b=1;
#endregion
}

after merge, will cause #region count and #endregion count not match

If classA has an inner class, the result of the merge may create an additional outer inner class.