If Cell.setValidityList() tries to find a reusable ContentValidationElement, the thread hangs in an endless loop if more than one node childs exists.
The following szenario reproduces the problem:
- create new SpreadsheetDocument
- append a new sheet
- set same value list to first cell of two rows
- set value list to a third row -> thread hangs
Its a bug in Cell.getContentValidationEle(). The appended patches contain a test to reproduce it and the bugfix as well.