After Debugging the Payroll Schema  article, I thought it would be interesting to share some of the  places where I set a break-point when I need to investigate a recurrent issue.
If you think the issue is a bug, you may search correction SAP notes using the abap code as a search term in case there has been a recent change on the same.

1. Splits are generated apparently for no reason:

Include RPCHRT09_FILL_APER_FOR_REGULAR

FORM fill_aper_for_regular_payroll

2. Retroactivity or is triggered apparently for no reason:

CLAS CL_HR_PAYROLL_MAIN METH DETERMINE_RETRODAYS

3. Different currencies involved in payroll calculation.

Currency in IT0009 <> Payroll currency.

Include RPCGET00_FUP0009

PERFORM convert_to_foreign_currency

Currrency in IT0015 / IT0014 / IT0267 <> Payroll currency

Include RPCGET00_FUP0015 / RPCGET00_FUP0014 / RPCGET00_FUP0267

PERFORM convert_to_local_currency

4. Why splits in table WPBP are created.

Normally it’s obvious but.

Include RPCGET00_FUWPBP

PROVIDE massn massg stat1 stat2 stat3         FROM p0000
persg persk bukrs werks btrtl kostl plans gsber
*         vdsk1 ansvh orgeh stell               from p0001  “P30K097081
“XMU2001/08/29
*         vdsk1 ansvh orgeh stell fistl geber FROM p0001 “P30K097081  ”
vdsk1 ansvh orgeh stell                        “XMU2001/08/29
fistl geber fkber grant_nbr         FROM p0001 “XMU2001/08/29
dysch wkwdy arbst                                 “S11K123108
schkz empct zterf                     FROM p0007
*                                     FROM p0027
subty
trfar trfgb trfgr trfst
*         bsgrd divgv                           FROM p0008    “N0329415
bsgrd divgv waers                     FROM p0008  “N0329415
*         KUSWG KUSPE KUSCH KURFN KUSKL KUKFB                 YUI060391
*         KUDIV KULSA                             FROM P0049  YUI060391
* new for funds management new with XULAHRK015788
*                                     FROM i_fund_for_provide
BETWEEN pn-begda AND pn-endda
WHERE p0027-kstar EQ ’01  ‘ AND
p0008-subty EQ l_use_subtype.

Also:

RPCBU309_OPWPBPC

Include RPCBU309_OPWPBPC

PERFORM split_wpbp_and_it TABLES sdates.