ActiveX Combobox listrows property being ignored

I have a set of comboboxes set to list the sheetnames in a document for calculating some stuff (it's not important.
The problem I am having is that no matter what I do to the listrows property the dropdown list is only 1 item high with tiny scroll arrows when I first click the dropdown arrow. If I unexpand the list and re-expand it again it works fine it just isn't happy when it is first selected.

I'm pretty sure it is down to the list being cleared and repopulated each time the combobox is selected so the listrow max is set to 0 before the list is populated and is not refreshed untill after the dropdown has expanded with a row count of 0. If I select the box before clicking the dropdown arrow it works fine (again I believe because the list has been populated before the dropdown is expanded).

Anyone know how to resolve this? (I could set the showdropbutton property to when focus but I would rather have a proper solution).