Trendscape forms

I have a client, on version V2.50. Within the system they have a trendscape form. Sometimes when the form is opened the column headings of the righthand side textbox, SourceExpr = CurrForm.Matrix.MatrixRec.Code, appears blank. If you scroll across and back the colum headings reappear. Sometimes this doesn’t work and the users zup file has to be deleted. I suspect it is something to do with filters and the zup file. Not all users get the problem and the occurance appears to be totally random. Has anyone else experienced this with trendscape forms?