- Open _common_data/clustal/non_unique_row_names.aln.
- Open and close the "Tree Settings" tab of the Options Panel.
- Select the first sequence in the alignment.
- Press Delete 2 times.
- Crash.
Bug explanation:
The MsaEditor and its children live longer than the TreeOptionsWidget, so the signal triggers even if it's already been removed. Since this is not a signal receiver here, but just a captured pointer, there is no check for its validity.