Powershell with Switch and Regex - Replace substring based on next line

On a daily basis I have to process text files (MT940)in our finance system from about ten different bank accounts. To be able to improve the processing of the bank statements, I want to enrich these files. Basically by replacing the bank transaction code (in this example NMSC) with something else or making to the transaction description (:86: lines) more readable. The file may look like:

:20:
:25:MHCBNL2AXXX/0265515777
:28C:27/
:60F:C200207EUR100196,42
:61:2002070207D1326,80NMSCTOPF1450330305SDD TOPF1450330305
:86:FR601810010131670100ARVAL FRANCE BBB200210505254134245678815001141818
:61:2108240824D1976,72NMSCTOPF2140474819//GABK002SCT TOPF2123454819--AA--
:86:ABCWNLXXOBGNL953123450004107181ARIANA GRANDED127139012108000003Gehalt  8/2021--AA--
:61:2108240824D3581,11NMSCTOPF2140474818//GABK006SCT TOPF2140474818--BB--
:86:ABCANLWWXXXNL402011456789701498LADY GAGAD127139012108000002Gehalt  8/2021--BB--
:61:2108240824D3742,44NMSCTOPF2140474817//GABK004SCT TOPF2140474817--CC--
:86:CXWANLWWAT201456787210005293SHEERAN EDD127139012108000001Gehalt  8/2021--CC--
:61:2105250525D3742,44NMSCTOPF2025434704SCT TOPF2025434704
:86:CXWANLWWAT201456787210005293SHEERAN EDGCMS000039851534Salary
:61:2105250525D3581,11NMSCTOPF2025434705SCT TOPF2025434705
:86:ABCANLWWXXXNL402011456789701498LADY GAGAGCMS000039851545Salary
:61:2105250525D1976,72NMSCTOPF2025434706SCT TOPF2025434706
:86:ABCWNLXXOBGNL953123450004107181ARIANA GRANDEGCMS000039851576Salary
:62F:C200207EUR39752,98

I want to do the following:

1. In lines that start with :61: and have SDD in them, I want to replace NMSC by RDDT.
2. If a line that starts with :86: and has the word Salary or Gehalt in them, I want to replace NMSC in the previous line (the one that starts with :61:) with SALA.

I do this with the following:

    switch -Regex ($MT940)  
    {
    '^:61:[0-9]{1,6}.+D\d+\,?\d*NMSCTOPF\d+SDD TOPF\d*'        
    { $_ -replace  'NMSC' ,'RDDT' }
    '^:61:[0-9]{1,6}[0-9]{4}D[0-9]+\,[0-9]?[0-9]?NMSCTOPF\d+.+SCT.+'                 
    {$saved = $_ ; continue}
    '^:86:.+salar.+|^:86:.+Gehalt.+'       
    {$saved -replace "NMSC" , 'SALA' ;$_}  
    default                               
    { $_ } # unrelated line, pass through
    } 

This gives the following result:

>>:20:
>>:25:XXXXXXXXXXXXXXXXXXXXXXX
>>:28C:27
>>:60F:C200207EUR100000,00
>>:61:2012311231D0000,1RDDTTOPF1234567890SDD TOPF1234567890
>>:86:FR1234567890ARVAL FRANCE
>>:61:2108240824D0000,01SALATOPF2140474819//GABK002SCT TOPF2123454819--AA--
>>:86:ARIANA GRANDED12713901210Gehalt 8/2021--AA--
>>:61:2108240824D0000,01SALATOPF2140474818//GABK006SCT TOPF2140474818--BB--
>>:86:LADY GAGA127139012108000002Gehalt 8/2021--BB--
>>:61:2108240824D0000,01SALATOPF2140474817//GABK004SCT TOPF2140474817--CC--
>>:86:SHEERAN EDD127139012108000001Gehalt  8/2021--CC--
>>:61:2108240824D0000,01NMSCTOPF2025434704SCT TOPF2025434704      AA
**>>:61:2108240824D0000,01SALATOPF2140474817//GABK004SCT TOPF2140474817--CC--**
>>:86:SHEERAN EDGCMS000039851534Salary      AA
>>:61:2108240824D0000,01NMSCTOPF2025434705SCT TOPF2025434705      BB
**>>:61:2108240824D0000,01SALATOPF2140474817//GABK004SCT TOPF2140474817--CC--**
>>:86:ABCANLWWXXXNL402011456789701498LADY GAGAGCMS000039851545Salary      BB
>>:61:2108240824D0000,01MSCTOPF2025434706SCT TOPF2025434706      CC
**>>:61:2108240824D0000,01SALATOPF2140474817//GABK004SCT TOPF2140474817--CC--**
>>:86:ABCWNLXXOBGNL953123450004107181ARIANA GRANDEGCMS000039851576Salary      CC
>>:61:2012311231D0000,1RDDTTOPF0987654321SDD TOPF0987654321
>>:86:FR1234567890ARVAL FRANCE
>>:62F:C200207EUR39752,98

Question: What I do not understand is why the lines marked between ** are inserted.