QB Issue Resolution:

Retained earnings is an account that holds (until you distribute it) last years net income – except for sole proprietors

If  you back dated that deposit to sometime in the last fiscal year – that is the reason it went to RE

If you are using income accounts named by year as your comment seems to indicate – that is not normal – on the first day of the new fiscal year the income and expense accounts for last year are rolled up into retained earnings so current transaction post to income and expense for this years reporting.

Resolution for Issue 'Made a deposit and it went into retained earnings. Other deposits made to this account do not go into retained earnings. How do I get that with the rest of the deposits?' available: Yes (Solved).
Source: Intuit Community forum.

Made a deposit and it went into retained earnings. Other deposits made to this account do not go into retained earnings. How do I get that with the rest of the deposits?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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