Problems setting correct day on Sekonda Automatic 25 Jewels 1970s watch ?

I have a Sekonda automatic watch 25 jewels - USSR. I believe it was made in the 1970s. I'm having problems setting the day - when it gets to Wednesday it then changes to Thursday in a few hours time before reaching 12am.
It has a crown which moves the hands and there is a button for changing the date. The date changes OK - it is just the day which is proving to difficult to set properly.

Any help much appreciated.