Hi Jens
From SAP library, the example shows that the usage of predicate is with the EX operator, so maybe it is a limitation.
Integration Directory - SAP Library
Maybe you can try to combine your two conditions in the predicate and use it with the EX operator
(SHPMNT05/IDOC/E1EDT20/E1EDL20/E1EDL37/E1EDL49/E1EDL50[XSIQUALF='EEIVERF' and VLABDATA = '01'] EX)
Rgds
Eng Swee