Is Windows Phone picking up smartphone market share in America? Two leading research firms offer opposite views on the matter. The new comScore numbers are fairly shocking — they show Microsoft’s smartphone market share dipping to 3% in the three-month period ending in April, from 3.1% in the period ending in January. This would be pretty devastating considering AT&T and Verizon both have offered fairly robust Windows Phone marketing support since December. But wait! Just few days earlier, Kantar Worldpanel stated that Windows Phone’s share in America jumped to 5.6% during the three months ending in April, up significantly from 3.2% in the period ending in January.

That looks like a pretty big move. Kantar went so far as to title its recent report “Windows Growth Continues.” So the question of whether Windows Phone is growing its market share or not is rather central.

Of course, different research houses have different methods and their tracking numbers are never going to be identical. But two leading smartphone research companies now have completely opposite views on one of the biggest questions of the year: Is Windows Phone gaining ground or not?

This is a pretty rare situation. One key distinction here is that comScore measures subscriber base share while Kantar watches smartphone sales market share. It is theoretically possible that the Windows Phone subscriber base may have stalled out even as its share of phone sales has grown under certain circumstances. For example, if former Windows Phone owners upgrade fervently while the platform fails to gain new users from rival operating systems, then this is feasible.

The problem with this scenario is that Kantar is specifically stating that only 25% of buyers of new Windows Phone models had a Windows smartphone previously — most of them are switching from feature phones or Android smartphones. That is why it’s so hard to reconcile Kantar’s upbeat view of Windows Phone’s expansion with comScore’s negativity. How would it be possible to have Windows Phone gaining new converts from rival operating systems this strongly without Windows Phone’s subscriber base expanding?

One of these firms has likely screwed up royally.