I've been discussing this with Orit (adrian on CC) and in Portugal I've noticed a similar case that may or may not have relation to this.
What I see is when a station never had GPL, it randomly fails to set the value. First I thought it was something related to the number of decimal digits (0.8 instead of 0.888 for example), but then it revealed not being relate to that. Today I got the opposite case - was able to set GPL to 9.999!. Our price ranges are €0.5 to €1.999 in Portugal.
So far I also had a feeling it was only related to GPL, because I never got any issue with the other prices - Diesel, 95 and 98 - which turns this all even more confusing.
Anyway, just to mention that Orit and Adrian should probably verify it there is any relation between these two cases and if there is any issue with the validation algorithm