I am tracing the Green family from John and Ellen Green [nee Thompson]. I have found a few occasions when children or grandchildren of John and Ellen have been baptised twice.

For example, Rachel Green, daughter of John and Ellen, appears to have been baptised twice according to the Isle of Man Parish Registers 1598-2009:
1. 10 May 1846 at St. Barnabas, Braddan.
2. 30 June 1846. This entry is preceded with "(Sub conditione).

Please explain.