SSAS Tabular. MDX slow when reporting high cardinality columns.

Even with small fact tables( ~20 million rows) MDX is extremely slow when there are high cardinality columns in the body of the report.

e.g. The DAX query is subsecond.

Evaluate
SUMMARIZE (
CALCULATETABLE('Posted Entry',
'Cost Centre'[COST_CENTRE_ID]="981224" 
, 'Vendor'[VENDOR_NU]="100001"
,'Posted Entry'[DR_CR]="S")
,'Posted Entry'[DOCUMENT_ID]
,'Posted Entry'[DOCUMENT_LINE_DS]
,'Posted Entry'[TAX_CODE_ID]
,"Posted Amount",[GL Amount]
,"Document Count",[Document Count]
,"Record Count",[Row Count]
,"Document Line Count",[Document Line Count]
,"Vendor Count",[Vendor Count]
)
order by 
'Posted Entry'[GL Amount] desc

The MDX equivalent takes 1 minute 13 seconds.

Select 
{ [Measures].[Document Count],[Measures].[Document Line Count],[Measures].[GL Amount], [Measures].[Row Count],[Measures].[Vendor Count]} On Columns ,
NON EMPTY [Posted Entry].[DOCUMENT_ID_LINE].[DOCUMENT_ID_LINE].AllMembers * [Posted Entry].[DOCUMENT_LINE_DS].[DOCUMENT_LINE_DS].AllMembers * [Posted Entry].[TAX_CODE_ID].[TAX_CODE_ID].AllMembers On Rows 
From [Scrambled Posted Entry]
WHERE ( [Cost Centre].[COST_CENTRE_ID].&[981224] ,[Vendor].[VENDOR_NU].&[100001] ,{[Posted Entry].[DR_CR].&[S]})

I've tried this under 2012 SP1 and it is still a problem. The slow MDX happens when there is a high cardinality column in the rows and selection is done on joined tables. DAX performs well; MDX doesn't. Using client generated MDX or bigger fact tables makes the situation worse.

Is there a go fast switch for MDX in Tabular models?