CVTSD2SS weird memory operand discrimination

[Madoc]

None of these asm lines will compile:

Code: Pascal  [Select][+][-]

1. procedure foo(const a: double);
2. asm
3.    cvtsd2ss xmm0, [a]
4.  
5.    cvtsd2ss xmm0, qword [rcx]
6.  
7.    cvtsd2ss xmm0, qword ptr [rcx]

With errors that seem to vary depending on the type of a, including:

Error: Asm: [cvtsd2ss reg??,mem128] invalid combination of opcode and operands

These however work just fine:

Code: Pascal  [Select][+][-]

1.   cvtsd2ss xmm0, [rcx]
2.  
3.   movq     xmm0, [a]
4.   cvtsd2ss xmm0, xmm0

 cvtpd2ps works just fine in all cases, as well as all other instructions I've used so far.