find causes stack overflow

I managed to have this happen when drag/dropping a structure onto an alignment during the '3 pfam alignments, one structure' conservation visualisation on structure exercise.

Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
at jalview.datamodel.Alignment.getHeight(Alignment.java:707)
at jalview.analysis.Finder.getSequence(Finder.java:230)
at jalview.analysis.Finder.nextSequence(Finder.java:358)
at jalview.analysis.Finder.getSequence(Finder.java:239)
at jalview.analysis.Finder.nextSequence(Finder.java:358)
at jalview.analysis.Finder.getSequence(Finder.java:239)
at jalview.analysis.Finder.nextSequence(Finder.java:358)

Steps to reproduce:
1. Import uniref50.fa
2. Copy and paste the first four sequences to a new alignment window.
3. Open 'Find' and search for FER1_SPIOL in the new alignment. click away the 'Finished searching' dialog, but keep the Find dialog open.
4. Select FER1_SPIOL in the first alignment.
5. Click 'Find' in the find dialog, FER1_SPIOL will be found.
6. Click 'Find' again - jalview will wait a bit - and eventually return control without any other dialog appearing, and without FER1_SPIOL being highlighted as found. If the console is open, the stackoverflow error will be shown - otherwise check the log file.