Extraneous and incorrect C output

[Wall-AF]

I have the following assembly (illustrated with the pcode):

   11e0:12bc 8b 5e ee     038           MOV        BX,word ptr [BP + pElems_?nOffset]
                                                      $U1100:2 = INT_ADD BP, 0xffee:2
                                                      $U3400:4 = CALLOTHER "segment", SS, $U1100:2
                                                      $U7900:2 = LOAD ram($U3400:4)
                                                      BX = COPY $U7900:2
   11e0:12bf 66 26 0f     038           MOVZX      EAX,word ptr ES:[BX]
             b7 07
                                                      $U3800:4 = CALLOTHER "segment", ES, BX
                                                      $U7980:2 = LOAD ram($U3800:4)
                                                      EAX = INT_ZEXT $U7980:2
   11e0:12c4 66 50        038           PUSH       EAX
                                                      $U9600:4 = COPY EAX
                                                      SP = INT_SUB SP, 4:2
                                                      $U9780:4 = CALLOTHER "segment", SS, SP
                                                      STORE ram($U9780:4), $U9600:4
   11e0:12c6 66 26 83     03c           CMP        dword ptr ES:[pElems_nSizeData_SI],0x0
             3c 00
                                                      $U3800:4 = CALLOTHER "segment", ES, SI
                                                      $U7a80:4 = LOAD ram($U3800:4)
                                                      CF = INT_LESS $U7a80:4, 0:4
                                                      $U7a80:4 = LOAD ram($U3800:4)
                                                      OF = INT_SBORROW $U7a80:4, 0:4
                                                      $U7a80:4 = LOAD ram($U3800:4)
                                                      $U1e700:4 = INT_SUB $U7a80:4, 0:4
                                                      SF = INT_SLESS $U1e700:4, 0:4
                                                      ZF = INT_EQUAL $U1e700:4, 0:4
                                                      $Udc80:4 = INT_AND $U1e700:4, 0xff:4
                                                      $Udd00:1 = POPCOUNT $Udc80:4
                                                      $Udd80:1 = INT_AND $Udd00:1, 1:1
                                                      PF = INT_EQUAL $Udd80:1, 0:1
   11e0:12cb 74 06        03c           JZ         LAB_11e0_12d3
                                                      CBRANCH *[ram]0x11e012d3:4, ZF
   11e0:12cd 66 26 8b 04  03c           MOV        EAX,dword ptr ES:[pElems_nSizeData_SI]
                                                      $U3800:4 = CALLOTHER "segment", ES, SI
                                                      $U7a00:4 = LOAD ram($U3800:4)
                                                      EAX = COPY $U7a00:4
   11e0:12d1 eb 06        03c           JMP        LAB_11e0_12d9
                                                      BRANCH *[ram]0x11e012d9:4
                             LAB_11e0_12d3                                   XREF[1]:     11e0:12cb(j)  
   11e0:12d3 66 b8 00     03c           MOV        EAX,0x10000
             00 01 00
                                                      EAX = COPY 0x10000:4
                             LAB_11e0_12d9                                   XREF[1]:     11e0:12d1(j)  
   11e0:12d9 66 5a        03c           POP        EDX
                                                      $Ua080:4 = CALLOTHER "segment", SS, SP
                                                      EDX = LOAD ram($Ua080:4)
                                                      SP = INT_ADD SP, 4:2
   11e0:12db 66 2b c2     038           SUB        EAX,EDX
                                                      CF = INT_LESS EAX, EDX
                                                      OF = INT_SBORROW EAX, EDX
                                                      EAX = INT_SUB EAX, EDX
                                                      SF = INT_SLESS EAX, 0:4
                                                      ZF = INT_EQUAL EAX, 0:4
                                                      $Udc80:4 = INT_AND EAX, 0xff:4
                                                      $Udd00:1 = POPCOUNT $Udc80:4
                                                      $Udd80:1 = INT_AND $Udd00:1, 1:1
                                                      PF = INT_EQUAL $Udd80:1, 0:1

and this produces:

            uVar1 = *pElems_?nOffset;
            if (*pElems_nSizeData_SI == 0) {
               uVar2 = 0x10000;
            }
            else {
               uVar2 = *pElems_nSizeData_SI;
            } 
           uVar2 -= uVar1 & 0xff | (uint)(byte)((ulong)uVar1 >> 8) << 8;

Why on earth does the line uVar2 -= uVar1 & 0xff | (uint)(byte)((ulong)uVar1 >> 8) << 8; contain & 0xff | (uint)(byte)((ulong)uVar1 >> 8) << 8 extra garbage?

Is there some incorrect sleigh stuff or is it a bug?