Issue with covering shorts in 0.4.22

[pendragon3]

The gui in windows Ver 0.4.22 64-bit seems to have a problem with respect to covering operations. (I haven't tried the other versions of 0.4.22.) So, I tried partially paying off some BitUSD for a grandfathered short position. Normally, paying off some of the owed BitUSD should raise the margin call price because the short position becomes better collateralized.

However, instead of raising the call price, my transaction actually lowered the call price! Is this a known issue?