Can confirm in 19w09a, and this is total bullshit. I finally managed to find and tame 4 cats, and of them fully 3 managed to drown themselves.
No. The maps display fine, but a banner placed in the last map pixel on any edge can't be marked. I made a quick example in a superflat creative world to better demonstrate it:
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The pink banners can be marked on their respective maps. The white and black banners can't be marked on either map.
In this case, with the maps zoomed all the way in, it's easily circumventable by just moving the banner over a block, but it's always the outer map-pixel, so on a max zoomed out map it's a 16-block strip on each side of the map, for a total gap of 32 blocks. That can be a major problem if you happened to build right on the edge!
The world itself (for 19w08b) is attached if you want to see for yourself.
Confirmed 1.12. (Not surprising, as it was still in the pres, but good to note)
I think that's intended: redstone torches burn out if you attempt to toggle them too quickly.
Also happens for things placed in 19w09a.