Tiles not laid out properly in split-map view

[brucecrevensten]

STR are vague but roughly I suspect that if there are tile requests in flight when split maps are activated, they may not draw in the right place.

Along the lines of,

• click to open a new layer that is coming from Geoserver which you haven't opened before (i.e. no local cache)
• immediately click the Show two maps...

Expected: map looks fine? Actual: