Possible Bug in File Handling

This Code deletes the content of the File test1.txt if it existed before. I noticed this because of a typo in one of my scripts. Tested with v.2.45 on Vista SP2 64Bit and XP SP3

Outfile test.exe
Var File1
Var File2
RequestExecutionLevel user
Section "Main"
    SetOutPath "EXEDIR"
    FileOpen "$File1" "$EXEDIR\test1.txt" w
    StrCpy "$File2" "$EXEDIR\test2.txt"
    FileWrite "$File2" "Hello World"
    FileClose "$File1"
SectionEnd 

Why is the File test1.txt altered? FileWrite is referring to the wrong handle.

Why is the File test1.txt altered?

The file is altered because your script contains this line

FileOpen "$File1" "$EXEDIR\test1.txt" w

The Users Manual explains why this happens:

4.9.5.2 FileOpen
user_var(handle output) filename openmode
... The openmode should be one of "r" (read) "w" (write, all contents of file are destroyed) or "a" (append, meaning opened for both read and write, contents preserved).