BW sub-process-chain, sometimes some steps were executed twice - why?

we have an bw metachain (bw sub-process-chain) with name: "PC_AK_Bewegungsdaten", 

which is used two times

1)

one time this chain "PC_AK_Bewegungsdaten" is called from our (so called) evening bw process-chain,

2)

the second time this chain "PC_AK_Bewegungsdaten" is called from our (so called) morning bw process-chain,

the problem is, that only when this bw metachain (bw sub-process-chain) with name: "PC_AK_Bewegungsdaten

is called from the morning bw-process-chain, some steps are executed twice, and we did not know, why?

is this bw metachain (bw sub-process-chain) with name: "PC_AK_Bewegungsdaten

executed within the evening bw-process-chain, the identical process-chain steps are only executed once!

here some details:

a) the bw metachain (bw sub-process-chain) with name: "PC_AK_Bewegungsdaten",

b) the chain above is called two times:

c)  Executed in the morning bw process chain, e.g. the step 2LIS_11_VAITEM_ME_DELTA_ERP

     is executed twice - why ?

anybody any idea?