Excel disappears from the taskbar in Excel2003
 

I am having problem with Excel 2003 when I have few spreadsheets opened. I
can work on spreadsheets fine, however when I minimize and maximize it few
times Excel button disappears from the taskbar and can be recalled using
Alt+Tab combination or by going to task manager selecting Excel from
Applications and pressing "Switch to" button. This is completly random
behaviour. Is there any way to prevent it from disappearing?