Unexpected handling of labels

FASMW 1.49 (interface 0.90) seems to handle some label names (specifically: E2, and E6 -- there may be more) in an unexpected way. I don't see anything special about these names, maybe someone can explain it.

Here is sample code, derived from the FASM example HELLO.ASM:

Code:

include '%include%/win32ax.inc'

.data
E2      db 'Title',0
E6      db 'Text',0
_E2     db 'Title',0
_E6     db 'Text',0

.code
start:  invoke  MessageBox,HWND_DESKTOP,E2,E6,MB_OK
        invoke  MessageBox,HWND_DESKTOP,_E2,_E6,MB_OK
        invoke  ExitProcess,0
.end start

Here is the disassembly:

Code:

00402000                    start:
00402000 6A00                   push    0
00402002 6A00                   push    0
00402004 6A00                   push    0
00402006 6A00                   push    0
00402008 FF156A304000           call    dword ptr [MessageBoxA]
0040200E 6A00                   push    0
00402010 6811104000             push    401011h
00402015 680B104000             push    40100Bh
0040201A 6A00                   push    0
0040201C FF156A304000           call    dword ptr [MessageBoxA]
00402022 6A00                   push    0
00402024 FF1554304000           call    dword ptr [ExitProcess]

Regards, Frank