Sometimes "browse tool" (in menu) is not working. Why ?

[doupsy at wanadoo.fr]

Hello,

I have a stack that I made first with Hypercard, and transformed  
since few years by Revolution.
This stack work perfectly, but sometimes, I cannot choose "Browse  
Tool" int the Tool Menu( and the same if I click in "Browse Tool" in  
the tools palette, the browse tool is selected, but in the tools  
menu, the browse tool is not selected).
I must restart the application Revolution and all is OK.
Why ?
What is this problem ?

I am under OS X 10.3 on a G4. I have Revolution 2.1.2

Thanks

Edouard