In a custom MDI frame, PowerBuilder does not size the client area so you must size it in the script for the Resize event in the frame. 

When you create and save a MDI frame, PowerBuilder creates a control called mdi_1. PowerBuilder uses mdi_1 to identify the client area of the frame (the area that holds the sheets).  mdi_1 displays in the list of objects in the PowerScript Painter Paste Objects drop-down list box. 

To size or resize the client area when the frame is opened or resized, write a script for the Resize event in the frame window that determines the size of the frame and then sizes the client area (mdi_1) appropriately.

TIP:   mdi_1 is not a reserved word, but should be used with caution.

For example, this script sizes the client area for the frame w_mdi_custom2. The frame has a series of CommandButtons across the top below the menu and MicroHelp at the bottom of the frame.

int  nWidth, nHeight

// Obtain the width and height of the workspace
nWidth = WorkSpaceWidth (w_mdi_custom2)
nHeight = WorkSpaceHeight (w_mdi_custom2)

// Calculate workspace between the CommandButtons
// and the MicroHelp. cb_1 is the CommandButton 
// nearest the top left-corner of the frame.
nHeight = nHeight - (cb_1.y + cb_1.height)
nHeight = nHeight - (mdi_1.microhelpheight)

// Move the upper-left corner of the client area (mdi_1)
// to the bottom-left corner of the CommandButton (cb_1).
Move (mdi_1, 0, cb_1.height)

// Resize the client area.  The frame window has a line
// below the buttons at the top of the window so add 4
// to nHeight to allow for the line.
Resize (mdi_1, nWidth, nHeight + 4)

Note:MicroHelpHeight is an attribute of mdi_1 that PowerBuilder sets when you select a window type for your MDI window.  If you select MDI Frame, there is no MicroHelp and MicroHelpHeight is 0; if you select MDI Frame with MicroHelp, MicroHelpHeight is the height of the MicroHelp.