Help with count function in DMR

[cognos05]

I am using count function in my report on 2 columns and if I sort my rep column then my report layout behaves in a odd manner.(sorting is done by clicking sort by ascending, also tried selecting reps and then click sorting and choose the account column and then say descending and used order function)

I have Distributor-> Regions-> Reps nested in rows and they r from same hierarchy with different levels.
Columns showing YTD, PriorYTD,YTD Change and sales as measure.

Now I am showing 2 calculated columns one will just give the number of accounts corresponding to each rep .

SO I have used the expression AccountCount : count([YTD] within set children(currentmember(rows hierarchy))

Second Expression Negative Account Count for each rep :  Count( [YTD]within set filter(children(currentMember(row hierarchy)),[YTD Change]<0))

Have I used the count expression correctly , is count supported in dimensional reporting ? On Sorting my rep based on Account count or negative count my data in the row gets collapsed and the rep data item is not shown or disappeared.

Any help on this is appreciated.

Thanks,
Nithya