Screen goes blank white on launching JOSM

[alexkemp]

1. Startup computer
2. System update via Synaptic
3. (no synaptic updates, no other programs active)
4. Launch JOSM
5. (Normal wait at beginning)
6. Screen goes blank white
7. only option is to switch off/restart computer

This first happened whilst working in JOSM. I had selected a node, then screen went blood-red (same colour as the selected node). On next going into JOSM it first reported corrupt config (or some such) and that it would create a default config (+ preferences.xml_backup iirc; it is a zero-byte file). Then delay, then screen went white & so on.

wtf??

I have zero knowledge of any changes of any kind before this event.

I'm a competent computer user + programmer, and am happy to bug-chase under direction. I cannot provide any status reports, etc. currently as cannot get into the program.

Would clearing ~/.josm help?

[Answer: no]
I renamed ~/.josm to ".josm-backup" then launched JOSM.
It at first appeared to be working normally. However, at some point near the end of the start-up sequence, the screen turned entirely light-blue & was frozen once again.

Having restarted & looking at ~/.josm it has an empty 'cache' dir + a zero-byte 'preferences.xml' & that is all. Help!

System:
JOSM: 10168 (latest stable)
System: Debian Jessie 8.4

 ~$ java -version
 java version "1.8.0_91"
 Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
 Java HotSpot(TM) Client VM (build 25.91-b14, mixed mode)