TDBCombolookup Not Dropping down enough

We have a fairly well populated Delphi 5 app that has about 25 Datasources
in a datamodule connected to a form, where the TdbLookupComboBox's have a
random drop down count when we click on them, where the data in each drop
down is fine, say we have 20 options from a lookup table the first time we
click on the dropdown it show 1 line with two stupid little up/down arrows,
then if we select one of the small arrors , close the box, then open the box
it now shows 5 lines, do it again then it shows say 12, then on and on
untill we hit the DropDownRow property in the property editor,

I have looked back through all my knowledgebase systems and can see this
problem many times but nobody has produced an answer yet?

Is it a STANDARD delphi bug in the professionl version ?