Odd Drop Down Box Behavior

I have a drop down box on a spreadsheet in a workbook with several
spreadsheets. For some reason the contents of the drop down box is beeing
bled through to other spreadsheets in the exact same cell reference that the
drop down box is linked to, replacing what may be in that cell. It happens
randomly yet often, and I have not been able to discern any patterrn or
catalyst. The contents and cell formatting are being transfered. It also
happens on other spreadsheets using the drop down box. This is an Active-X
box, not a forms box, using Excel 2007.

Anybody seen this?

Squeaky