Clock widget stopped to display time and date

Clock widget stopped to display sane data. I think it happened after setting clock to 24hour mode and adding date with long format. Now I have blank light-gray space in place of widget and calendar view displays table with positive and negative numbers, but not with month name anymore. System time checked from cli is correct.
Any clue how to make clock widget usable again?

Thanks in advance

That sounds like happening in a desktop environment. Which one?

Exactly, it is in KDE4 - version of most components is like “libkde4-4.14.18-10.3.x86_64”.