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The issue occurs using the 'Merge Selected Features' tool when there are geometrical errors in the features (not all are picked up by the 'check geometrical validity' tool).
In 2.2 Valmeria, the merge fails to complete. This is acceptable, as it alerts me that I need to fix geometrical issues with the features.
In 2.3 nightly build from 12th June, the merge fails to complete, and at least one of the features is deleted. This can be undone, but it is a worry, as the user might not notice on time.
Anyone experienced similar, or advice if I should report this somewhere?