OE Order Entry table expands outside window

SOLVED

Hi,  

We have a custom macro which uses the 2016 OE Order Entry form front-end with a bit of custom code to handle some odd edge cases in the background.

For some reason the table of line items in the custom macro version stretches off the edge of the window on the bottom and right hand sides, making the macro entirely unusable (See below) .
This does not occur on the same PCs when the standard OE Order Entry form is being run.

So far we have tried:
- Reinstalling Sage300
- Re-registering MSCOMCTL.ocx
- Changing screen resolution
- Running as admin

Does anyone know how to fix this issue? It is occurring across both Win7 & Win10, but only on 3 computers which have been set up recently.