Strange Shapes Generated

Firstly, this is a great set of data that I'm happy to have access to - thank you.

I've been validating some of the data and have seen some strange polygons created and wanted to know what the root cause of this is (whether I'm doing something wrong, etc)

Take for example the Lee Valley Velo Park in the London Olympic Village

QuadKey
031313131

GeoJSON

{"type": "Feature", "properties": { "height": 13.368171691894531, "confidence": -1.0},"geometry": {"type": "Polygon","coordinates": [[[-0.0157944811891353, 51.5498873613391], [-0.0150260252882228, 51.54981204486004], [-0.01432737688843, 51.55010193634923], [-0.0142696764511419, 51.55032957855235], [-0.0143002375035706, 51.550471440745774], [-0.014356194905103, 51.55047692506388], [-0.0143442665252391, 51.55048187447204], [-0.014487055323984, 51.55046997412536], [-0.0144380864679139, 51.55053708350929], [-0.0144016262879187, 51.550503106682434], [-0.0143764661721479, 51.550513546289885], [-0.0143894566669678, 51.550517212058246], [-0.0142963400004903, 51.55052496855504], [-0.0146877720281213, 51.55088973810615], [-0.0147126724344382, 51.55087940634456], [-0.0147352944973411, 51.55098441509665], [-0.015145624364965, 51.551024630568165], [-0.0154314963522073, 51.551000818062036], [-0.0154610816810541, 51.55088415044336], [-0.0155460087835846, 51.55087707248641], [-0.015393999752602, 51.5508621743923], [-0.0154913992232708, 51.5508540612036], [-0.0152974538954131, 51.55079934087585], [-0.0157401026437887, 51.55084272402034], [-0.0157342952068773, 51.55081576657256], [-0.0158801282427845, 51.55075525689982], [-0.0158274894931654, 51.55074040521631], [-0.0158615216231595, 51.55072628444183], [-0.0159005322309236, 51.55076263780404], [-0.0162377862542717, 51.55030051949016], [-0.0157944811891353, 51.5498873613391]]]}}

However, this yields

Also, in other more simple shapes, the polygon regularly seems off-center, e.g. the following GeoJSON from the same quadkey

{"type": "Feature", "properties": { "height": 7.860638618469238, "confidence": -1.0},"geometry": {"type": "Polygon","coordinates": [[[-0.0274372725260852, 51.5481362747604], [-0.0272214088040679, 51.547928701888935], [-0.0268442539518987, 51.54808039258931], [-0.027034435718174, 51.54826324954267], [-0.027223555193634, 51.5481871947816], [-0.0272492415839887, 51.54821189185068], [-0.0274372725260852, 51.5481362747604]]]}}

Yields

Any help would be appreciated, thanks in advance

Start by reproducing the Lee Valley Velo Park examples using QuadKey 031313131, the supplied GeoJSON, and the attached images. Compare the generated polygons with the source data to determine why shapes are distorted or off-center; done means identifying the root cause and documenting or correcting the affected output.