[WD21] Weird integer in composite key problem (no replies)

We have a data file (MyDataFile) with several fields, some of them:
SCode (Text, String 20)
NLineNo (Numeric, Integer +-999 999 999 --> 4-byte)
DStartDate (Date, yyymmdd)
It also has a composite key:
IND_Code_LineNo_StartDate (with all 3 fields of above)

Looking at the data in HFSQL Control Center this index seems to be filled correctly. I even reindexed the table to be sure.

Now I'm trying to access data with this index:

nLineNo is int = 30000
HFilter(MyDataFile,IND_Code_LineNo_StartDate,["S12345",nLineNo,hMinVal], "S12345",nLineNo,hMaxVal])
I'm not getting any result.

This workaround does work and gets me the desired result:
HFilter(MyDataFile,IND_Code_LineNo_StartDate,["S12345",hMinVal], "S12345",hMaxVal], "NLineNo="+nLineNo)

I'm now using the workaround, but what is wrong with the first variant?

I even tried using
minVal is buffer = HBuildKeyValue(MyDataFile,IND_Code_LineNo_StartDate,"S12345",nLineNo,hMinVal)
maxVal is buffer = HBuildKeyValue(MyDataFile,IND_Code_LineNo_StartDate,"S12345",nLineNo,hMaxVal)
HFilter(MyDataFile,IND_Code_LineNo_StartDate, minVal, maxVal)
In the debugwindow I get the following as values:
minVal: "S12345<0><0><0><0><0><0><0><0><0><0><0><0><0><0>0u<0><0><0>"
maxVal: "S12345<0><0><0><0><0><0><0><0><0><0><0><0><0><0>0u<0><0>ÿ"
On first glance, I would say this is definitely wrong. there should be 30000 instead of 0u. But why?

So has anyone any ideas, what I'm missing?

Thanks a lot for your answer.