UNDO Space: used way bigger than total (no replies)

Hi,

we experienced - during a mass delete action - a undo space full.

Since then our monitoring barks at us with crazy big usage percentages.

---
ndb14 undo space usage too high: PROBLEM
Undo space usage (node id 3): 156180628937.61 %
---

So looking at the checked value shows:
mysql> select total,used, used/total as percentage from ndbinfo.logspaces where log_type='DD-UNDO' and node_id = "3";
+-------------+----------------------+-----------------+
| total | used | percentage |
+-------------+----------------------+-----------------+
| 11811160064 | 18446744071955687784 | 1561806289.3061 |
+-------------+----------------------+-----------------+
1 row in set (0.02 sec)

mysql>

There is either some magic going on - or a overrun of a variable...

Best regards