You already know how exchange rate is derived for posting based on user's time zone. However, you find such logic does not work for journal entry voucher.
SAP Business ByDesign
Reproducing the Issue
You have your time zone as UTC+8 in your personal settings. You create an journal entry voucher and found system does not picks the exchange rate based on yoru time zone.
In business transaction posting, for example, you create a supplier invoice with posting date on 25.07.2017. When creating the document, the system always appends time as 23:59:59 to the posting date, hence 25.07.2017 23:59:59. Since you have time zone as UTC+8, the UTC time to be considered for exchange rate is 25.07.2017 15:59:59. So system picks the exchange rate table (in UTC) for the valid rate on 25.07.2017 15:59:59 UTC.
However, journal entry voucher alwayws takes UTC time to pick valid exchange rate. In this example, it picks the exchange rate valid on 25.07.2017 23:59:59 UTC instead.
The approach now is to maintain the exchange rate manually in journal entry voucher creation.
exchange rate, time zone, journal entry voucher, 汇率，用户时区，时区，手工凭证 , KBA , AP-ACC-GL , General Ledger Account , Problem